The rules for serial (and monographic series) title changes are subdivided into “major” and “minor” changes. For serials, a major change requires a new bibliographic record. A minor change is generally handled by updating the existing record with a 246 field. For series statements, a major change requires a new series authority record; a minor change is generally handled with a reference (4XX) on the SAR.
In RDA, major changes to the title proper can be found under RDA 18.104.22.168.1 and the corresponding LC-PCC PS. Under AACR2 changes to title proper were covered under 21.2A and the corresponding LC rule interpretation (LCRI).