1) Assuming you put blast/2.6.0 into your default modules using module save, how do you undo that change?
$ module list
Currently Loaded Modules:
1) intel/17.0.4 3) git/2.9.0 5) python/2.7.13 7) TACC
2) impi/17.0.3 4) autotools/1.1 6) xalt/1.7.7 8) blast/2.6.0
$ module unload blast
$ module list
Currently Loaded Modules:
1) intel/17.0.4 2) impi/17.0.3 3) git/2.9.0 4) autotools/1.1 5) python/2.7.13 6) xalt/1.7.7 7) TACC
$ module save
Log out and log back in to see if it worked.