[Tails-dev] Possible make own tails with older TOR

How involved would it be for me to make (for personal use) a version of TAILS based on 1.3 but with an OLDER version of TOR (namely version that had Firefox ESR 24.0 or something like that).... Is that possible? (security implications aside)... Or alternatively, keep the same TOR 4.0.4 code, but swap it out (the browser implementation) with Firefox 24/28.0 instead? Any of these above can be realitively easily done?