I do like Kamikaze does.
Why bother opening all those menus when all you need is the mouse in PVR.
Mostly I highlight all the notes and drag them up with the velocity smart tool. This is the red area as shown in the diagram of a midi note in PRV.
Here's a little trick I use to do what the OP is asking ( sort of)
My digital drum kit often records at very uneven velocities. I want to preserve some of this but not all.
The snare track- Say the highest value is 127 and the lowest is 80
I like my snare maxing around 107
127 is too much and 60 is too little so dragging it all down -20 won't cut it.
So I look for a note that is around 107 highlight the whole snare part using the left hand keyboard GUI and drag them all to max
let go, grab again now I drag them all down to 107. ( -20 )
the 127 will now be 107 , The 80 and all between 107 are preserved. But I have now evened out all the overs.
If I want a whole track, like bass to be the same then I grab the lowest value note and do the same. All the notes get squished to max and then you simply just drag it back down to where you want it.
All this with a few strokes of the mouse.. fast.
Keep in mind that Velocity IS NOT volume. Example is Ample Bass passed 120 it turns into a Slap sound. Velocity's purpose is to manipulate timber. Piano stuck softly sounds totally different than a piano hit at max. Most sounds in the VST world respond to higher velocity with harsher timber.
So it's important to understand this when messing with velocity.
The perfect tone your after might be between 80 and 112.