It's not that bad... part of the system changes are related to stuff that doesn't come up often, changes to races & feats can be seen as basically setting-specific, and with regard to classes it's likely that each PC is affected only by a couple of house rules anyway.
The question is how do you manage with your players? Were these house rules added to the game gradually as your group was playing along, letting the players get used to the changes one at a time? Or did you design your set of house rules on your own, and then delivered them at once for your players to read? The latter is often disorienting, because new players won't know the reason behind your house rules, and may thus see them as pointless.
By the way, your format of presentation is really nice. Can you tell what word processor, graphical effects and fonts did you use? I wrote some fantasy setting conversion material that I would like to share on ENWorld but I would like to improve the look of it. (Feel free to PM me so that we don't get out of topic from your thread)
I basically rewrite the entire PHB. And I've done it multiple times...
It goes back to the '80s when at the time I owned everything that had released for D&D, including magazines, 3rd-party stuff, etc., not to mention a lot of non-D&D stuff. If we found a rule, class, whatever that we liked then it was fair game. So initially it was just to compile it all in one place, and correct blatant issues, contradictions, overpowered or poorly designed things, and also to incorporate rules into a coherent set. It was really the only way to make it usable for the group, which did change a bit over time. Even if it was printed on a dot-matrix printer.
The campaign continued through 2, 2.5, 3, and 3.5 (with an attempt at 4e), and so I had to constantly update and redo it.
With D&D Next and 5e I started with RAW. But the problem here became the drastic changes from the feel and rules of the past campaign. The rules are always modified with an eye toward campaign consistency, what makes sense in the game world, and being able to create the scenes that we want to be able to ("I am not left handed," the NPC who is too injured to help, and many other examples). I use existing 5e mechanics almost exclusively, borrowing things like the exhaustion track and death saves for other purposes. There are other drastically changed things (like sorcerers) that are specifically based on what we think they should be.
All of the rules (RAW or house rules) are always up for discussion, and the players often take an active part. If something's not working, we change it. If we change something that would alter a character, it's up to the player to decide if we grandfather in their character or change it. While it may seem excessive, the goal is really for the rules to intrude on the game as little as possible. So I initiate most of them (the current group is almost all new players), and they are based on 35+ years of tweaking and about 30 years for this campaign itself. I'm also always looking at whether a change is needed, or even if the rule itself is needed.
An example is (yet another) modification to hit points/injuries sparked by a new player that didn't like the fact that there aren't any consequences for having low hit points. I have rules for injuries which have long-term effects, but hadn't addressed the fact that if you don't suffer any of those types of things, then 1 hp is the same as 100 hp in terms of the state of the character. So I provided a new alternative that shifts to the exhaustion track at 0 hp instead of dying. The exhaustion track is already engaged if you're wounded, and in both cases you make a save each turn, with failure worsening by 1 level, and 3 non-consecutive successes "stopping the bleeding." You don't get better but you stop getting worse. There's no more dying rule, since this is essentially 3 successful saves before 6 failed saves.
So the question is what DC do we want to use for the saves? Do you want a 40%, 35%, or 25% chance of survival if you don't receive any assistance through mundane or magical healing? The answer came back at...25%. Unanimously. If you're reduced to 0 hp, or you suffer a wound via a critical hit (you get a saving throw to avoid it), then you should have only a 25% chance to survive unless you stop what you're doing and deal with it.
In other threads, I've had people say they'd walk away from my table if we used the core rules with the simple addition of 1 level of exhaustion each time you are dropped to 0 hp.
And while in discussions like that, I've had a number of people stating that they'd walk away from a table with this rule or that, I've yet to have one walk away from mine. But I think that has far more to do with talking with people and setting expectations than it does anything else.
As for how they are introduced, it's pretty much as the game plays. I have the material available for them to access online, and I am also happy to print materials too. Most of the time I don't address specific rules until we have to. So they come up via play initially, and I'll explain what the rule is at the time, and if there are objections we'll deal with it then, or go with it and address changes we want to make outside of the game. For example, for the last few years we haven't used initiative at all (except as an occasional opposed check). The intention for this campaign was a new variant, but we haven't used it at all yet. It hasn't seemed like it was needed, and even the experienced players didn't even question it. The combats continue to evolve logically - for example, one of the halflings startled a flock of cockatrices, and so they scattered, attacking whatever was between them and escape. The characters were fairly well spread out, so obviously we resolved attacks as the flock spread and the characters closed toward the halfling. No initiative, and no rounds, just actions occurring naturally.
I'm hanging onto the combat rules, because they have worked well, and it's really difficult to write-up what we do for somebody else to use, although the version using initiative and incremental segments is basically the same thing with a mechanical way to keep track of things.
