Which vcsels are used in different modes?
Is it feasible to use only two vcsels in medium and far mode?
Near mode uses 2 VCSELs, the ones on the sides of the lens, while medium and far use all 4 VCSELs.
It all depends on the range you want to achieve - 2 VCSELs are feasible for medium and far but the range will be reduced. It's hard to say by how much without measuring the optical power.