This is a problem I come across regularly and feel there's room to save a step or two.
1.) Field data comes back from GPS or field notes in a table containing UTM Zone, Easting, and Northing fields. There may be multiple UTM Zones (e.g. Zone A and B).
2.) Display XY data, using Zone A as CRS.
3.) Export all data to a single feature class, using the chosen UTM Zone (A).
4.) Set Data Frame CRS to Zone B.
5.) Select and export records in Zone B to new feature class, using Data Frame CRS.
6.) Start editing and delete records in Zone B from the feature class in Zone A.
7.) Merge Zone A and Zone B feature classes into a single feature class with common CRS.
As you can see, this is somewhat convoluted. How do you handle tabular data in multiple CRSes?