BattleTag Change

Is there any way i can preview my BattleTag change?
I currently have RiveLLa with a 4 digit code and would like to change it. If I do that now, there is no guarantee for me to get another 4 digit code and I possibly could end up with a 5 digit one. I would like to match my BattleTag with my Discord username and # via nitro.

I know it’s not possible to only change your digit code but is there any possible way to preview the new BattleTag before assigning or to change it back if it doesn’t work out the way I like it? Thanks in advance for your response.