I will translate the first segment into 100 ס"מ
and Studio will suggest for the next segment 200 cm
but I would expect it to suggest 200 ס"מ
That is, I would expect Studio to incorporate the Auto-Substitute into the TM.
Can this be done (I know of at least one other CAT tool that does it), is it just a setting thing?
Yes, Trados does it by default. Please go to Options menu > Editor> [select] Auto-propagate, Concordance; in Translation Memory menu [and your Project setting tabs] [select] Add TM, Concordance, Update, Lookup.