Is it possible to render the same sequence again ??

Do i simply load all the JPG's output files from the previous Light Room session back into light room, then export to LR Timelapse somehow ?

I want to do this becsaue i want to create 2 different output videos. One in Medium format, and one in Ultra HQ 4K...

That's what the "File/Render" function in LRTimelapse is for. No need to use Lightroom again - just open the intermediary sequence in the LRTimelapse render dialog and render again.
For this to work, you have to remove the tick on "Delete temporary sequence after rendering" when you first render in LRT, otherwise the intermediary sequence gets deleted.

Questions on the above instructions, what is the " intermediary sequence" I need to open, you mean the LRTimelapse project that I want to redo a new video for?...