While you can get a very small reduction in trigger pull by using a reduced power mainspring, there are good reasons not to do that. The mainspring has far more to do with correct operation of the gun than just pushing the hammer. I am easily able to get a sub 4# trigger pull using a standard 23# mainspring, aka hammer spring.
The correct way to lighten the trigger is to first clean up the hammer and sear interface, stone the hammer hooks to no lower than .020", stone the front and back of the disconnector paddle, and do other general cleanup of burrs and roughness. Then, the big deal, tune the sear spring. Specifically the left and center legs. The center leg has to have enough tension to resist trigger bounce when dropping the slide with finger off the trigger, and the left (sear) leg can be lightened up to the point that it still provides tension to the sear throughout the sears range of operational motion. Under 2# is possible if everything else is done along with tuning the spring. 4#-5# should be doable even with just tuning the spring. Of course the quality of the pull won't be nearly as good as doing a proper trigger job. In fact creep and gritty feeling may become more apparent. As usual, when doing anything to the fire control parts, you must reverify correct safety function before you call it done.
If you are not comfortable, skilled, and/or equipped to do the other work you can still tune the sear spring and you will get more out of that than playing with a lighter mainspring. The 1911 forum will provide as much detail as you care to absorb on this subject and anything else 1911 specific that you care to know.