Patcher doesn't work without an active account, however.
Otherwise, yea, you could do what WoodElvinDruid said. But with an active account, it will probably work without deleting anything, other than all of the *.log* files (basically: EQ_Missing_Files.log*, EQPatch.log*, Everquest.log*, and LaunghPad.log*).
Yther Ore.