Yes.
It is easy to house rule and I strongly encourage it.
Just keep house ruling simple in the spirit of C&C. For example:
20 very simplified feats from 3e
Allow cleave and power attack for any pcs with strength primes and two-handed weapons
Weapon specialization/mastery from Rules Compendium and 1e Arcana Unearthed
Set a massive damage threshhold=con score like Omega World (?)
Open-ended damage for certain very vulnerable situations (e.g. casting in melee, fleeing combat, grappling an armed foe)
Adopted Mind Witch class (slightly weakened) from Monte Cook's game
Made up (simple) rules for grappling, out of turn dodge and evade, and covering up shield
Created specialty priests similar to 2e by deity (using mostly Greyhawk deities)
Used the starting social class rules (elaborated upon) from the Gygax' Yggsburgh book
Tweaked the C&C barbarian class with a couple of features from Conan and 1E
Added 100 spells from past editions and Monte Cook's game
Will probably add tweaked 4e rules on different abilities with different specialized weapons
Anyways, my goal has basically been to have a game that is: 1) very simple at its core so that you could explain the essence to a 10 year old in 15 minutes and 2) has a customization flavor for each player based on the good (simple) ideas and classes from a variety of sources over the past twenty years. Simple, open ended continuously tweakable or evolveable.
Lets discuss feats as an example. If 3.5e has hundreds of feats, some of which are complex or esoteric that can be easily daisy chained to destroy game balance, then I want to do the 80:20 rule by grabbing the 20 or so shortest but most practical or interesting ones that allow people to customize their characters but don't daisy chain much. Here are seven examples of flavorful feats that aren't too complex or crazily daisy chainable with each other:
Slippery Mind (get a second save vs. mind and emotional control one round later). Make a cha prime the prerequisite to select.
Great Fervour (wis prime prerequisite; reroll one save per day if an extremely devout pc verbally invokes his deity for aid).
Weak Spot or Bullseye feat (wis and dex prime prerequisites; if you are unencumbered and spend one round observing a humanoid or animal and you make a successful wis check with opposed levels, you discern a weak spot in that foe and you do open-ended damage with a thrown weapon with which you are specialized).
Ambidexterity (dex prime prerequisite, cut penalty with two weapon fighting in half)
Finesse Attack (dex prime or int prime prerequisite; use either or both your int mod or dex mod for to hit and damage bonuses in melee rather than your str bonus with a dagger or short sword with which you are specialized).
Roll With The Blow (prerequisite: dex prime, if you have open space behind you and you make a successful dex check, you take half damage from all bludgeoning attacks if you can roll backwards 5' per each ten points of damage avoided; you also treat falls for which you are prepared as if they were from 10' less distance).
Out of Turn Evade (prerequisite dex prime, prior to the time that the foe rolls his to hit dice against you, you may forego your action in the round if you haven't already gone and it is not a surprise or sneak attack, and you gain a +5 to AC vs. all attacks from that one foe or a +5 on your save vs. the breath weapon or magical attack that has a dex related save from that one foe).
You can find some of my tweaks and other people's ideas on the Troll Lords website forums Under The Rules and The Chaos and on the Dragonsfoot Boards under the C&C forums.
