If an instructor changes forms to fit his philosophy does that make him a bad instructor?

That depends on what you want and what the instructor claims to teach. Over 25 years ago I was at a seminar with Shogo Kuniba teaching kata and bunki. As Master Kunbia went around the room he would show a few pressure point applications and some joint locking that fit the form. Unbelievable but the host/dojo owner would follow Kuniba changing the techniques to useless nonsense. Only a fool would miss this and I can't believe Kuniba didn't flip out. later I cornered the dojo owner/instructor and demanded an explanation to what he was doing. His reply was "the techniques being taught did not fit my philosophy so I changed them" I then asked what is your school's philosophy? Reply was "I teach martial fitness and basic self defense, not fighting or techniques that can kill or seriously injure one for life" I could not understand so I asked why bring an Okinawan Master to your school. His Answer "legitimate lineage" Soooo what does all this mean? Always ask what a school teaches and what is it's end goal because if you don't you may end up some where that you do NOT want be, even if the school belongs to a legit National organization with famous instructors.

Does this make the instructor bad? Only you can answer that...

If the forms he changed are nonsense then he would be a bad instructor.

Depending on the martial art style, forms are passed down from one instructor to the next person in the lineage. What about all the other good students who make really good teachers but are not the successor of the lineage? Should they just not teach? I don't think so. Many went off and made their own forms and taught. This was meant to keep people from being divided how a form should be taught in a style because no two people will teach the same form exactly the same way. It's also an explanation why the kata with the same name in each style are different. It really depends on who makes the changes, what changes, why and how much they know and understand.

Depends on what is his philosophy. Changing a forms in itself is no indicator of a good or bad instructor. Both good ones and bad ones do it.

It might make an electic commitment to be a great teacher and parent

if you feel uncomfortable, then yes. no pain no gain, so bear for couple of weeks, then if he doesn't suit/you don't see improvements then he is bad

Can you be more specific?