Percentage increase or decrease in tempo

It is actually much easier than that.

Make a PLE preset like this:

This will behave on any tempo events you select.

You can remove the Property “Is Selected” line if you want to change the tempo events for the entire track.

And of course if you want different percentage amounts just change the math on the “Trim” line:

1.1 will multiply by 1.1 (10%)
1.06 would be 6%


Bear in mind that you cannot go to crazy extremes here as there are limits to the range of tempo.

You can find this, and many other PLE presets (free) on my GumRoad: