Check out the repluse moves on page 41 of the rules - although this doesn't fully clarify it - they must be read in conjunction with the movement rules. However, Phil did provide a clarification - see page 40 of the DBMM commentary version 4.1.4:
Repulse Outcome if Unable to Repulse Fully due to Bad Going
If a repulsed element has bad going within a tactical move and directly behind them and they have insufficient move to enter it (due to being slowed by reaching the bad going), then they recoil instead.
Committee, based on Phil Barker, DBMM List, message #42683
So my reading of this is that if you are sufficiently close to the bad terrain and your modified repluse move can put you into the terrain, then you yes you can repulse, albeit at the slower movement rate.
Andrew
