This is the case for loads of different objects and behaviours. I think in general, if you can set it by initially, you should be able to change it at runtime.
Most recent examples that have annoyed me: physics contact friction, particles fade colour.
I think all of these, even if you cant think of a use for it off the top of your head, are worth adding to just add more possibilities to projects made in construct.
After all, ideally construct needs to have as few limits on what it can produce as possible, and I've sometimes felt limited by not being able to change properties like these at runtime, because if you're going to use these behaviours or whatever you can't really work around it.