I was basing this query/request off the rules in the Core Rule book on page 549 (4th printing) and specifically the section on Adding new abilities on pg 553. There are rules there for adding new abilities, and one of the examples is adding Invisibility to a Ring of Protection +2 and the pricing for it. But it may be too difficult to implement, as you said. I'll fiddle around more with the Editor since that appears to be the only solution at this time. Thanks for replying!
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Thanks, also, ShadowChemosh for replying. You snuck in while I was writing the above.