did anyone use other code languages as kids? If so what were they called and what were the rules?
My mom knew one where p's were inserted into words. (I don't remember much more except that it was more complex than Pig Latin and she's asleep so I'll have to wait.)

For starters:

higgledy piggledy:
-- insert an unstressed hard "-igg-" sound between syllables (actually more a schwa than a short -i-): wiggOT diggID yiggOO siggAY?

never had a name that I know of:
-- insert the unstressed syllables "-ithigg-" (soft -th as in leather; unstressed): withiGOTT ditheGID yitheGOO sitheGAY?

Ubby-dubby, from ZOOM! (sometimes written Ubbi Dubbi)
-- insert an unstressed -ibb- between syllables: wubbAT dubbID yubbOO subbAY?

Variants I played with with my kids involved making the insertions stressed, instead of unstressed - a different task to unscramble, as it alters the "shape" of the words: wUBBat dUBBid yUBBoo sUBBay? etc.

I suspect the names were highly variable, the actual codes much less so.

Good thing you gave an example of what you meant by soft -th. The voiced versions always sound harder to me than the unvoiced versions.

Aren't they independent variables? "This" and ""throw" are both unvoiced THs, no?

This is voiced, throw unvoiced. Feel your throat while saying them.

Yes, but I can't remember if we called it ofa or whether I'm confusing it with wofa's name! Anyway, it was just like his higgledy-piggledy but with f's: where his is wiggOT diggID yiggOO siggAY?, ours was whaFOT diFID yuhFOO suhFAY?