How would I go about adding an ability modifier, that is not the class's spellcasting modifier, as a bonus to damage or healing on a homebrew spell?  For instance, if I wanted to make a spell that healed the target by 1d6 + the caster's constitution modifier, how would I go about doing that?

I don’t think you can unless the caster uses Von as their Spellcasting ability. That’s just how 5e is designed.

Thank you, but do you ever sleep? You are everywhere in the forums, seemingly at once.

Lol. Yes, I sleep.