You can rephrase the sentence by replacing the word 'but' with 'although' or 'however' while keeping the original meaning. For example:
- 'I would definitely go there again although only when it's not busy.'
- 'I would definitely go there again; however, only when it's not busy.'
Both sentences mean the same as the original, expressing that you like going there again, but your visit depends on it not being busy.