Change the timecode with ffmpeg in the middle of the track? I know you can change the timecode of a file with FFmpeg with the option –timecode. This modifies the whole timecode of the file starting from the  -timecode added. 

Can you change the timecode with FFmpeg in the middle of the file? Jumping to another timecode (always in the future). This can be useful with the –concat option. Merging a bunch of files into a unique file. Reflecting the actual time every isolated file was recorded.
Depending on your final use case, a non-standard way to deal with that would be to keep the original TC as LTC (audio TC) on an additional track. Concatenating clips would then preserve the original TCs on that separate track.