The license will remain same after upgrade to 7.x code. It is true that UR licensed PIX requires 128 MB of RAM for 7.x code. If you dont need UR features, you may contact email@example.com and request for a Restricted key, you'll need to send the "show version" of the firewall. As UR to R conversion is downgrade, you should get the activation-key for Restricted license from licensing team.
Alternatively, you may refer to following link for upgrading memory on your PIX-
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...