Where does the pipe enter the house?
It might be better to joint iron to Hep2o outside, then bring that in. You get a new pipe which is very difficult to freeze and not subject to future failure and leaks.
If necessary you can bring water pipe in above floor using a special box outside which is stuffed with closed-cell extruded insulation, BES sell them, about =A380 and likewise there is low depth insulation available too for about =A319 per 1m length.
Removing a brick or two is trivial if you have a mains drill and a
20-38mm sintered diamond core drill. You just stitch drill through the brick, push in a wide slotted screwdriver and twist the brick into pieces. Very little vibration re vulnerable pipework compared to an SDS (depends on the skill of the user and hardness of the bricks). Of course you need a new brick to go back, frankly I would use celotex or extruded polystyrene behind the pipe where possible - rising CW main against cold solid walls are not a great idea. Never expanded polystyrene because it is porous to water (increasing risk of freezing).
Remember any pipe will freeze where the average temperature is below zero even if insulated and no water is moving, simply because insulation merely slows the rate of heat loss - it does not prevent it completely. The proper pipe insulation is the closed cell foamed rubber stuff, but should be protected against UV.