Why couldn't you just not undo it, and have it read/write twice? This wouldn't be a problem if you're accessing normal ram, like the prologue and epilogue of a function. Add a comment to the manual saying to not use this instruction when reading/writing hardware registers where accessing it changes state.
Not all instructions are re-startable. ldm/stm that writes back to the base register is only re-startable if the write-back and the update to PC are last.
The microcontroller-scale cores have a few extra bits in the control/status register that govern restart of an interrupted ldm/stm or IT (if-then, a form of hammock predication).
