I have downloaded a few gates over time, most before OFB came out so they don't have the locking functions, now I'm wondering if it's possible to change that in SimPE? Or does it involve exporting the mesh and re-importing it onto a different Maxis gate?

Check to see if that gate has been updated.

It hasn't, and if the creator has no intention of updating? I did think of all that

With doors, the change in OFB was global in such a way that all doors, old and new, automatically had the locking option. I wasn't aware it didn't happen with custom gates. If that's the case, I'm pretty sure it can't be fixed in a simple way in SimPE.

Edited to add: Actually, I may have been wrong. There does seem to be an easy fix for existing gates, although, I'm not sure if the locking actually works apart from adding the interaction.

How to add the locking interaction (experimental, I haven't really tested this thoroughly): Open the gate package in SimPE. Click on Object Data under the Resource Tree (make sure you're in Plugin view tab). Of the Object Data listed in the box on the right, click on the one with the shortest name. Then, click on the Raw Data tab. Select "decimal" of the options on top of the Raw Data screen, and look for a line called "Interaction Table ID". For a pre-OFB gate, the value is probably -1. Change the value to 4, then click Commit and save the package. Now the gate should have the locking interaction in the game. But, I still haven't tested if it actually works, or if it only adds the pie menu. It might need some further editing to make it work propely, I don't know yet.

Thank you IgnorantBliss! I'll try this out and see what the outcome is. :D

EDIT: Okay so, regardless of what object I open (I've tested half dozen or so) everything under the RAW Data tab shows up blank. I've messed around in RAW Data before I installed the newest SimPE version. My settings are set to advanced, any reason for this?