time machine use for Mac OS Mojave

[ujvalshah1]

I am installing Mac OS Mojave but I am backing up my laptop using time machine so I can use it when I want to down grade from the beta version but I have only one external hard drive and I have a doubt time machine will format my external drive so I am copying the files I needed to another laptop so can I copy all the files again back to the drive so copying the files again to the backed up drive would it create any problems while using the hard drive again as backup while downgrading ????