SRS - layer with two valid EPSG codes

[Stefanie Weykam]

> Hi list members,
> 
I have a polygon layer, a mesh witch fits to exact coordinates on the UTM
grid. 
If the datum is changed, the mesh should still fit to the original
coordinates and should not be reprojected.

I guess, I could work around this in our own application, but how do I
advertise this layer with several valid EPSG codes to clients?

> Thanks in advance,
> Stefanie
>