I have a few objects that have really many multisubobject slots and I would need to change texture in all of those. Is there a better way to do that than simply going all the slots through manually. If I could even change some master gamma value and it would change all the slots in one go. That would be nice too. I am using old sphere editor I haven’t used slate version ever.
Then you should start learning slate editor, because map instancing is a trivial thing in SME. As for the gamma thing, try this script: https://www.turbosquid.com/FullPreview/Index.cfm/ID/911001
Ideally this could be achieved simply by dragging the multimaterial into a Corona Mix Mtl performing some action in combination with another material.
Unfortunately multimaterials are poorly supported in Corona ATM. I hope this will change sometime soon 
try this script if it suit to your needs, it can edit selected nodes in slate editor
https://forum.corona-renderer.com/ Batch material edit
Thanks for replies. I will test those scripts for sure. I also tested slate editor and was shocked how much faster that is versus the old editor. I changed 12 textures in a few seconds while in old editor it would have been tedious task. For some reason old editor is also slow but slate seems to lightning fast.