How to double tempo for tempo detected track

This is what I did:

I imported an mp3 to a new audio track
I performed tempo detection
I added midi (instrument) tracks to play along in sync with the autio track

This all sounds great! Unfortunately the score of the midi tracks are unreadable because they contain a lot of 16nd and 32nd notes and rests.

What I want to do now is to somehow double the tempo of the project and at the same time double the length of all the notes so that the 32nd notes become 16ds and the 16nd notes become 8ths etc. The socre will then become much more readable.

Is this possible?

A complication is that, because of the tempo detection, the project contains a tempo track with a lot of tempo events so I cannot simply double the tempo.

If I can solve this by somehow changing the display tempo in the score editor I would also be happy.