functions – Changing the zone number in “UTMZone11” as used in GeoGridPosition

I can compute which UTM zone a point is in, given its longitude. I want to convert the geographic coordinates (latitude, longitude) to UTM in WGS84. This seems to involve my inserting a coordinate system spec like “UTMZone11” (e.g., utm = GeoGridPosition(GeoPosition({lat, long, elev}), “UTMZone11”)

If the next record contains a coordinate that is in a different UTM zone, how can I change the 11 in “UTMZone11” to the different zone number? Is there some sort of mask or dummy variable or other practice/strategy for changing the number within the “UTMZone11”?