Not sure what you mean be 'experimenting'. Githyanki is already a race in 5E. Vampire spawn as well. Werebear is a CR5 creature so that's not going to be an option.
There are rules in 5e for characters being infected by Lycanthropy, including werebears and weretigers, don't confused the example were creatures provided in the MM with the rules for players infacred by tge disease (and there are rules for PCs being infected).
