While my framework does have a couple stats that allow for altering hemogen max, I've found that the way Rimworld handles max hemogen is so prone to breaking that I decided to avoid making a full range of them, especially due to the fact that there aren't abilities with a high enough cost to warrant messing with it. Genes in other mods may alter hemogen max, but you'd have to check the details of those mods to find out.

Is adding genes that alter hemogen capacity possible?

There isn't really a way to multiply hemogen loss, just offset it. Plus, I found that removing the food need was impossible to balance as that functionally removed one of the key challenges of the game, so I don't really plan on creating genes that remove the food or mood needs.

how about a gene that remove food need, but increase hemogen need *2?

An All in One has been made . It will be updated in the future, but most of my planned easy genes have been made.