Yes you can feed the Selinites more than once, but you need to "flush" their digestive systems by adding water to their 'mush mixture' in the kitchen, there is a nozzle for adding water to the mixture in the vats. Then you can feed them something else......
Don't forget to check in inventory your (not sure of title now) "stumbling around" (?) it shows every experiment you have tried and each seedling and hybrid you have made at least once. I think each item raises your score a little bit, not sure. Am still playing game second time and had a strange experience at the end. Forgot to make and add the potash to the "pot" on my shell and suffocated to death, but also it froze my game and I could not get a reaction from my cursor, could not open my inventory or anything had to get out of the game and go back to my last save to redo ending. Very strange reaction to my "death"
Love, Betty Lou