the reason the manual says to zip tie it is to close the system. when the lever is pulled the ports to the reservoir are blocked. this means that the system is of fixed volume and the piston in the slave cylinder cannot move.
if you do not zip tie it, the piston in the slave will creep out (there's a spring inside that will push it out) and will draw fluid from the reservoir and potentially pull air into the system. this is the cause of all the "i changed sprockets and now much clutch doesn't work" posts. there are thousands of them because people didn't follow procedure.
to make installation easier, zip tie the lever, then crack the bleed nipple at the slave to bleed the pressure off. this will keep the piston in a resting position where it can't creep out, but it will also keep it at the retracted position, not the extended position, so putting the cover back on will be easy as you don't have to disengage the clutch with the cover going on.
then when you are done, before you release the lever, open the reservoir and carefully watch the level as you slowly release the lever. if the level goes too low simply top it up. (when you release the lever you must fill the master from the reservoir as the slave has been bled off)
simple as that really.