There are multiple ways as you suggested.
You can Bypass Assign a single footswitch with multiple blocks to it to enable lead sound, and assign MIDI CC# 0-69 to it.
ie. overdrive, parametric eq with mid push and 5db gain boost.
Or you can change Snapshots with MIDI CC# 69, 0-7, as you said.
Both work equally well.
edit:
If you want to change a parameter (Gain, Volume) on a already ON block via MIDI you would use Controller Assign.
So there, three ways to activate Lead sound with MIDI in a single patch.
Which way is 'better' is completely up to you.