Firethorn pruning

I'm having the house re-pointed and have a couple of firethorns, pruned
to about 3' wide, which I have nurtured so far to about 12' against the
wall and I don't want to lose them. They have fairly straight central
stems and I intend to prune them back as close to the stem as is
reasonable so that I can then release the ties and carefully lay them
back so as to provide access for the brickies. Anyone know how close I
could reasonably go at this time of year without causing irrepairable