[tsatsos]

I've tried acetone (the strong one) a few times this way and the first result was the same.
When the boots swell leave them to dry and just wait, they will shrink in a couple of days once dry.

 

[tsatsos]

It works on all vinyl parts, but not all parts react the same so be careful!
Some types of vinyl dry plastic hard afterwards. With Dragon heads also works fine.
The basic procedure is (1) dip the part in acetone (2) when it swells and becomes soft (20 minutes max for big parts like heads, boots less time for sure) take out and leave it to dry. In a few days you are done.