Advanced macro format required
Using variables requires that you use the advanced macro format for your macro (see Basic and advanced macro format). Therefore, if you want to add variables to a macro that is in the basic macro format, you must decide whether to convert the macro to the advanced macro format. If you have an old macro in the basic macro format that many users rely on and that works perfectly, you might want to leave the macro as it is.
However, remember that all recorded macros are recorded in the basic macro format. So, if you have recently recorded a macro and are beginning to develop it further, then you might simply not have gotten around to switching to the advanced macro format.