Even with the new CPE you can still do this. Go into Settings > Manage Custom Properties. From there, sort by Object, Select the property and choose Assign Values. You can select all the volumes you want to modify and the value you want to assign then submit. You can also export the property, make the changes you want, and import them.
Thank you so much, I wasn't seeing that button. Still prefer the old CPE but this gets me closer to liking it.