Well, all the transformation will wear off during an event, the reason is mainly technical because it will be a nightmare to resize the character sprite every time a girl would grow, especially when there is six girls into the mix. I don't say it's impossible to do, it can be done with custom code, but I don't want to mess with that and I want to keep the development simple for now. However, I plan to add a permanent growth for each girl if the MC had a strong bond with one of them, but it will happen only near the story end unfortunately.
As for the MC getting shrink, he is not so lucky, but don't worry, Patty won't keep the MC shrunk forever... even she loves to see the MC being a few inches tall standing on her fingernail.
Ah crap, I spoiled too much already. I will stop right there :)