To rename custom-defined functions:
From Enterprise View or a custom view, select an Essbase Server.
Right-click, and select Edit, and then Functions.
In the Custom Defined Function Manager window, select a function, and click Rename.
In the Rename Function dialog box, enter the new name for the function.
Optional: To overwrite a function that duplicates the name of the renamed function, select Overwrite existing function.
Click OK.
Essbase renames the function.
create function (MaxL) in the Oracle Essbase Technical Reference