The thing is, they were already shooting that lakorn anyway, it's just the news came out that they're rewriting the scripts. So it isn't like they finished filming the lakorn already and now they're redoing everything. In the end, it doesn't really matter that the scripts are changed, it has no big impact on La Ruk's filming schedule at all. Min and the rest of the cast were already scheduled to film Cinderella despite the script changes.
As to why they're changing the scripts, it's probably because some people aren't exactly happy with the current storyline. Polyplus tends to recycle their plots and stuff. A lot of people give ch7 grief for their filming while the lakorn is airing but this obviously shows how it can be beneficial. If there are changes that need to be made, then they can do it. They wouldn't be able to if it's a 100% stock lakorn.