A 36M is similar to having two 18Ms in one module, providing two banks of 18 cues whereas a 72M is similar to having four 18Ms in a single module, thereby providing four banks, once again each having 18 cues.
You can assign each bank to a specific channel, for example, bank, A assigned to channel 01, and bank B assigned to channel 02. Using the 18R2, you select a channel and fire accordingly
When scripting with a multi-bank module it is paramount to script accordingly. You will not be scripting for cues 1 through 72, but scripting for 1 through 18 four times with each having group of 18 having their own channel. Of course with a 36M you will have two banks of 18, but the scripting process is the same. For more information on scripting see Create and Load Scripts to the 18R2 Controller.