I see no reason why you cannot go deeper than 0.045" (within reason), however when recutting the seat take great care to select a seat cutter that only cuts the seat, and not the surrounding head area.
With care the SR cylinder head can have seat inserts fitted, but you need to be very careful in your selection of seat inserts, as the design of the ports is such that the seat insert will not be supported around its entire periphery if you bore the seat insert hole too deep.