There are three blocks in the Master BIM:
The block R (the remedial part for the one-year-master)
The block 1 (the first year of the two-years-master)
The block 2 (the central part of the cursus)
A student can either go through BlockR+Block2 (in minimum one year) or through Block1+Block2 (in minimum two years), depending on his background (see accessibility conditions).
The block 1 of the Master BIM is the same as the block 1 of the Master BBMC. This is so in order to get familiar with the biological experiments and data that will be analyzed during the block 2
As a result, it is just an administrative formality to go from M1 BBMC to M2 BIM, or the other way around, if one changes its mind during the first year.