Convert YYYYMM to MMMYY
Python 3, 70 bytes

from time import*
lambda s:strftime("%b%y",strptime(s,"%Y%m")).upper()


This uses the built-in strftime and strptime functions.

For 1 byte more, here's a version which parses the string manually:

lambda s:" JFMAMJJASONDAEAPAUUUECOENBRRYNLGPTVC"[int(s[4:])::12]+s[2:4]


This encodes the month names in an interesting way (thanks to Henry Gomersall for saving a byte).