Am I right in thinking I will transplant and after...

Hi @Bluntsallday! I would do it the same day, if you're confident about the rempotting. Indeed, a properly done transplantation has no impact at all on the growth, if you do it correctly your plant won't even notice. FIMing however is a serious surgery operation and will necessarily generate stress, plant will need a few days to understand what's happening, re-drive its apical dominance, and recover / create new growth. Hope this will help, keep us up-to-date and happy growing 👊

There's no reason for not doing it the same day, as long as the transplant is straight forward and the roots are not disturbed. In my third diary I trasnsplanted 2 plants during their 2nd week and FIMed right away.