Carefull, unless I misunderstand you, you ar emicing up two things.
Regions are independant from what happens on the timeline. You can create a gazillion regions and never place them on the timeline. This is actually the most common use. So, in this case the regions do not have any embedded timecode, except for the “original” one, which is already part of the BWF header.
If you want to embbed the project timecode (I.e. where the regions are placed on the timeline), you will have to inject a new timecode. Therefore you will have to bounce the regions into new, individual files. Otherwise you will have a conflict between the timecode of the original file (of which the region is part) and the new timecode (placement on timeline). You can quicly do that by selecting the regions, right-click and “bounce regions to folder”. After placing them on the timeline you can then perform a “conform” (pool).
Or when you regions are already on the timeline, right-click on them and perform “bounce” and then “conform”.