This would be for a Thermal Store system, for which flame modulation is
(in
theory) an unneccessary waste. On the other hand, I'm thinking I might be
better off just 'going with the flow' and getting a standard (modulating)
boiler regardless of the redundant fucntion.

There's no problem in using a modulating burner for this. Indeed, it can
actually be beneficial, as when the store gets nearly full, a non-modulating
one can start cycling on the boiler stat when the store stat is not yet
satisfied, particularly if the pump speed is fairly slow.

Christian.