What I was looking for was some "inline code". As "code" just displays whatever is written inside its "box", "as-is" without changing / interpreting / parsing anything, I was looking for the same effect, but "inline", not in a "box".
If the only purpose of this "pre" code is to add initial and ending spaces, and "tt" (or any additional BBcode) is still required for the rest of the text, then IMHO there is no real need for "pre", as I could still write the spaces outside "tt" as usual, as in:
teletype code with initial and ending space outside its code
" [tt]teletype code with initial and ending space outside its code[/tt] "
The displayed result is similar to the one originally intended, but the spaces are written outside the BBcode.
To be clear, I initially thought "tt" would be enough, but "tt" is not the same as "inline code"; and since the content between "tt" codes was/is still being parsed in one way or another, then I looked for an "inline code" (seen as "var" BBcode in some forums).
Now, if "pre" can really act as "inline code" (no parsing and without the need for "tt"), then "pre" could be useful in some posts. Otherwise, I seem to miss the point of the "pre" code.
Sometimes there is a need for an "inline code" because a "code" box interrupts the normal reading flow, making it more difficult to understand for the reader, and even "ugly".
Since getting an "inline code" available in the forum seems to be more time-consuming than what I expected, I'll probably keep using the well-known good ol' "code" box, just in case, to be sure that the code I want to display is 100% clear and that can be selected and copied exactly as intended. In some cases, the potential reader might need to re-read the post as a whole, but by using "code" I'll be (more) confident that the code itself is displayed (and potentially used) as intended.
I apologize for wasting your time.