2 sets of line wires?
The additional connection holes at the line terminals are provided to extend an unprotected circuit to a location that doesn't need GFCI protection or to a location that GFCI protection will be individually provided.

I don't know what the installation instruction included with your receptacle says, but step 6 in the Leviton Installation Instructions doesn't actually prohibit installation with more than 4 wires, but instructs to have a qualified electrician do the installation. This is probably an overly cautious step to make sure somebody doesn't inadvertently connect wires to the hot terminals that were previously connected to the load that serves a location where GFCI protection is required. It could also be remotely possibly addressing cubic inch fill limitations in NEC 314, but there is little evidence of that. 

Replacing wire for wire should work if it was previously working properly, but I am cautious to recommend that since nobody over the internet can completely determine that no areas being served by the unprotected hot are in areas that now require GFCI protection.