Well, yes, there is a better method.
Open Advanced - Display/Modify Templates.
Enter as name for your first template for example Insert # and enter as text just #.
Select in the drop down list the next template, enter as name Insert => and enter as text just =>.
Close the dialog with button OK. Now you can insert these templates from the menu Insert, from the Template List view, from a customized toolbar, from within a script or a macro. But that would not be helpful for you.
So open next Advanced - Configuration - Key Mapping, scroll down in the list of commands to InsertTemplate0 and assign the key # to this command. On the next command InsertTemplate1 assign the multi-key ## (one # in upper, one in lower field).
UltraEdit inserts now => when you press quickly ##. But when you just press # and wait the specified time in the key configuration dialog before continue typing, the character # is inserted.