If you're struggling for xp, just open UpgradePerks_AreYouSure.rpy in the "game" folder in a simple text editor.
Find the code block starting with
"screen Not_Enough_EXP:", look for the line under it that starts with
"action [" (line 323 in V0.15a) and replace it with:
Python:
action [ Hide("Not_Enough_EXP"), SetVariable("MC_EXP", MC_EXP + 500)]
Do the same for the code block starting with
"screen Not_Enough_EXP_SUPERPOWERS:", replacing the action line (line 344 in v0.15a) with:
Python:
action [ Hide("Not_Enough_EXP_SUPERPOWERS"), SetVariable("MC_EXP", MC_EXP + 1000)]
Make sure the indentation is correct, save and close the file, then start up the game.
This way, each time the game tells you that you don't have enough xp to buy a perk or superpower, it'll give you the xp you need.