For example, in current Solasta, I can see the "Sylvan Archer" feat in this game, which took some hints from the "Sharpshooter" feat of the PHB.
You have mastered ranged weapons and can make shots that others find impossible. You gain the following benefits:
• Attacking at long range doesn't impose disadvantage on your ranged weapon attack rolls.
• Your ranged weapons ignore half cover and three-quarters cover.
• Before you make a ranged attack with a ranged weapon with which you are proficient, you can choose to take a -5 penalty to the attack roll. If you do so and the attack hits, it deals +10 damage.
Sylvan Archer =
• Increase your Dexterity by 1 (Max 20) and ignore half and three-quarters cover when shooting with a bow.
Now, we can clearly see which part the Sylvan Archer get some hint from the Sharpshooter feat.
If we can homebrew some feats like the Sylvan Archer feat, we players could start our own brainstorming for alternative homebrew feats of Polearm Master, Great Weapon Master, Sentinel, Lucky, War Caster, etc...
I just wish to make sure about the guideline of such homebrew modification, how not to violate the WotC copyright. As far as I know, we cannot just copy and paste of contents and change the name of it and then call it "homebrewed one". There needs to be some degree of modficiation to become a proper "homebrew" for CRPG game software. But I'm not sure how much is good, and how much is not.
Let's say we homebrew our own GWM and Polearm Master for Solasta and begin brainstorming. What would be the safest modification of these feats for homebrew, and how much are we allowed to partially use the PHB feats?