itīs not so difficult.
viewport is allways showing the default uvmap called "map1". you can find it in the UV Editor in dropdown menu "UV Sets"
now do following ->
- in UV Editor open Polygons and hit "Create Empty UV Set"
- then "Copy UVs to UVS Set... -> new"
- delete history
now your original UVs are saved.
next U can switch to channel map1 again to create new UVs. or you might also duplicate your geometry, layout the UVs there and perform then a "Transfer Attributes" operation to copy UVs from first object to duped obj (you can move verts around and still transfer, but it does not work anymore after you added or deleted edges/verts/faces) - just for U to know..
after your UVs are saved and you created new UVs copy them into a new UV Set2. delete history and thatīs it. now you can swith between your sets.
if you like to use both sets at the same time for diffuse map and a tileable map you have to open the
Relationship Editor from Window dropdown menu - you may use "UV Linking -> UV-Centric". select your obj with 2 UVsets. itīll be loaded left with the shader right
you see your sets and your two textures (in case you mapped diffuse and maybe bumpmap)
link uvs to according maps. (in the hypershader you see that maya added a node called UVchooser)
everything starts and ends in the right place at the right time.