I put a frosty modifier on my boots, but I ended up just making another pair of boots because I'd constantly mess up my friend's farm every time I walked by it. Having a toggle key for that modifier would be great.

Maybe for others too, such as speedy and jump?

No toggle keys for modifiers. Accessories were made specifically for toggling, and those have very strict requirements to be made. Tinkers' does not have a toggle mechanic for their modifiers, so neither will this mod. Specifically for Frosty, the vanilla Frost Walker enchantment can not be toggled either. Having a set of armor that works universally for your needs because you can turn specific modifiers on and off defeats the purpose of tinkering with multiple sets depending on the situation.