This is exactly the problem I had with my old 2005 156 1.9JTD. Had a lovely remap but - especially in colder weather (I guess because the air is denser) - I would often get MCSF's with resultant limp mode. I enjoyed my remap so much, I actually put up with it, and became adept at turning the engine off and restarting while on the move...not for the fainthearted, and I wouldn't recommend it!
Well now I have a 2008 1.9JTDm GT 150bhp Cloverleaf and have had this remapped to 192bhp and 440Nm torque (higher than my old 156). There are NO problems whatsoever. I had both my remaps done at Red Dot Tuning in N. London and the head guy there, Augusto, said the reason was that the ECU in later variants of the 1.9 diesel is much more tunable and tweakable, so the error code could be prevented from being generated, therefore no limp mode.
But as has been suggested earlier on in this thread, maybe a pressure relief valve would do the trick? But of course, then you would presumably lose some of the grunt of the remap?