"choosing a bar" is probably for both objects already asked too much.
you could try using [filein] and search for byte FF 58 followed by a word 04 to read the signature. not sure how to find best at which time it occurs, or how to make us of that data later in [seq] or [detonate]
as long as the midi file is format 1 it should be possible to create a custom formatted tempo map (including tempo and signature changes , as long as they appear on MTrk 2 and above) from it within maxmsp for the use in maxmsp, but i dont have an example ready.
There has been an external called [SeqPlayer] for playing midi files, that allowed to define 'in and 'out points and therefore loop type 0.
I think Eric L Singer is the author.
It is still working for Intel ...