I view metagaming as unwanted because i value character integrity, if you recall my original post it was about gaining more genuine reactions from the players-as-character for more interesting roleplaying experiences, and in other situations such as fire-against-ogre or which-way-is-the-treasure-room-in-this-module-I’ve-already-played it’s really not that difficult to just roll a nature check first or flip a coin/keep quiet while the rest of the party decides, I just don’t think it’s necessary to metagame in most if any situations but it wasn’t the metagame angle I wanted to focus on.
Ok cool. Correct me if I'm wrong, you want player advice on how you, as a player, can avoid the temptation of Forbidden Knowledge. Yes I'm being a bit cheeky, hopefully it lightens the mood.
Well, again, assuming you want to avoid being a jerk and aren't acquiring Forbidden Knowledge for malicious ends, the two main camps I can see here are "It is fundamentally impossible to avoid having Forbidden Knowledge affect your decision making, so don't sweat it and just play your character as you will" vs "As long as you don't act on the Forbidden Knowledge, and play your character as true as you can, it's no sweat."
You seem to have the basics down, just... don't act on it as best you can. Go with the flow of the low roll. What does a 5 Diplomacy check look like from Gundar The Gallant? He's your character, thats up to you. Now the other ones, like investigation get a bit tricky so here's some things you can ask your DM to do, see if they go with it.
- Decide if you want things like Bluff/Insight/Diplomacy to be rolled before or after the play-acting happens, and be consistent on that. If it happens before, you can simply play out what a 3 diplomacy looks like from Gundahar the Gallant, he's your character after all. If your group decides on after (that old 'you get a bonus for good rp' style), ask the DM to make it a secret roll and have the NPC react on that, and well it's up to you then to decide if Gundahar thinks he did well or not, based on what the NPC is doing.
- Ask for things like Stealth to only be rolled when it would be immediately consequential. You start sneaking down a hallway, ok. You are sneaking. Oh, you round the corner and there's a patrol NOW you roll stealth. That way, well, it's not Forbidden Knowledge as Gundahar can immediately tell if he's been spotted or not, due to alarms and and gunshots coming at him.
- Ask the DM to use Passive Perception and Investigation and Insight. If the behind the screen NPC roll doesn't beat the Passive, then yeah Gundahar clocks the lie, the secret door, whatever. If the secret roll beats it, Gundahar and you have no idea anyway, Forbidden Knowledge avoided.
- Additionally, when actively searching for something, try to be specific in your characters actions so the DM can adjust DC's and whatnot as needed. I know this used to(?) be called "mother may I" style DMing but as long as they also have a fallback DC for general searching as well, it'll be fine. Also these can be secret checks too, for individuals. Or just a big group check anyway, so that whoever succeeds can just tell the other characters.
- This also helps on Insight checks. Don't just "roll insight" at people. Try to ask about specific things if you think the person is lying. Do you have any evidence they're lying? Ask about body language, are they nervous, sweating in a cold room etc.
- Ask your DM to tell you if they are running any specific modules upfront, so you can avoid Spoilers while reading threads like this one and let them know if you've already played through one ahead of time so they can either change the module, or find a new one.
If you're looking for DM advice, do that stuff. That stuff I just wrote? Do that. That's my advice on mitigating having Forbidden Knowledge affect your character choices. Oh, and bring back Take 20 from 3e. If you haven't heard of it before, it's basically "You can take a really almost absurdly long time to do something to make your roll count as a 20+your adds". If they want to comb every inch of the place in search of a trap or secret door or evidence of embezzlement let em. And then probably a random encounter or something, I don't know.