I've looked all over and can not find a for sure answer to this. Can you insert stacking modules into a Netgear GSM7252PS while the switch is still powered on? This switch is located in a production environment so downtime is hard to come by.
Netgear's official answer is to power off the device before adding HSM cards. From GSM7228PS/GSM7252PS Product Information | Answer | NETGEAR Support
What are the two I/O modules for?
There are three modules that are available for these module slots: AX741, AX742, AX743 and AX744. AX741 is for 10G XFP. Netgear offers both multi-mode and single mode XFP, AXM751 and AXM752 respectively. AX742 is the stacking adaptor that comes with short Infiniband cable to provide up to 12 Gigabit of bandwidth in one direction. And AX743 is for the newer 10 Gigabit SFP+ module. Netgear also offers AXM761 and AXM762 SFP+ for multi-mode and single mode fiber. And AX744 provides CX4 10-GbE interface. The I/O modules are not hot pluggable. You need to power off the switch, insert or move the modules, then power on the switch.