Modify Calling Function UDF Excel VBA

[Dave]

I have a Excel UDF in VBA and I need to datetime stamp the calling
function.

MyUDF(arg1, arg2, arg 3) -- this is entered by the user

In my vba code, I want to a modify this UDF when it is calculated to
add the stamp. This stamp needs to be visible to the end user.

MyUDF(arg1,arg2,arg3, 1/1/2005) -- this should be the result

Thanks,
Dave