How do you...
 

...make a water level control crate?

I know what you're talking about, it is actually done by placing water level events around any old crate so whenever you hit the crate you pass through the water level events too.

I knew that would work, but in the official level where it was first used, there was no water level event to speak of :<

Also, how do you create a spike boll that causes an access violation when you shoot it off?

As far as I know, there's no specific method except to have a whole lot of other spike bolls in the level. The odds of access violations increase with the number of spike bolls.

I used search and replace to find out how many spike bolls were in Mike's Painful Purple Place -- a whopping 7 =s

Well, it could be just a memory thing in general. :| Is it less prevalent in TSF than in 1.23?

Typically, I can shoot off as many bolls as I like unless I'm playing one of Mike's levels.