Hello.

User defined functions can be made available through Add-Ins... write your
code for the function, save it as an .xla file, use Tools-Add-ins to load the
addin, and the function you wrote is available to be used as any other
function.

Is it possible to similiarly use code modules through Add-Ins?

Write a utilitiy module, load the add-in, use the utility from another
file's code modules by calling the subroutine the as you would the code
modules were in the same workbook?

Thanks,
Mark