Riftweald Manor, Mercer Frey's house in Riften, will no longer be accessible before the Thieves Guild quest The Pursuit without console commands, as accessing it earlier and picking up his plans would cause the Hard Answers quest to not start and break the questline (removed a barrel 0003FFE6 from RiftenWorld RiftenCityEast 43,-24 that allowed early access) (UESP)
The original fix to stop players from breaking the Thieves Guild quest by taking Mercer's plans before the quest sends you there has been reworked to disable his plans inside the house rather than attempting to block roof access outside. [QUST:00021553:TG07, Script:QF_TG07_00021553:Stage 50](Bug #36238)
Due to the new improved fix listed now being in place the old fix listed could be removed. It's just some scenery, but still.