From what I know it is not possible in Studio. You need to export the TB, create a new definition based on the definition of your existing TB, but change the setting for "case sensitive" in step 3. Then import the TB content there.

I'm just testing, nothing else.

I've followed your comment but.. the QA result looks like caseInSensitive regardless of TB settings.
Following is done on the basis of caseSensitiveTB

and it reveals "Term Recognition" is caseBlind too.

Larroque Hervé

I don't believe this is possible in Trados Studio or MultiTerm.  The best thing... possibly... is to set the case sensitivity in autosuggest:

Given there is no automatic replacement of terms this might make things a little easier for placement at least?

Yes, Of course.

Ex)
Segment 1 has both UpperCase and LowerCase "Let/let"
On the other hand, 
Segment 2 has LowerCase "let" only.
My tool, only, reckon Case correctly.

It is a paid service, of course.