Homebrew, Custom, 3rd Party… whatever.

Yes! Please! Love it! DM approval!
D&D 5E, while not without its many foibles and flaws works on a number of core design principles that can cause character power imbalance *very quickly* if upset. Messing too much with things like Action/Bonus Action economy, the limitation of concentrating on only one spell at a time, etc, should NOT be taken lightly. And as always, when I discuss character power and balance it is from a PC vs PC point of view, not Party vs DM. I can *always* rebalance combat encounters, often on the fly… But leveling out overpowered characters by taking things away from them is not fun, nor is it fun to be the character struggling to achieve 10 damage per round, when the person next to you is doing 50, all other things being equal.. This will be exacerbated in adventuring parties with a range of levels of course, but that’s a horse of a different color.