Mixing Lithium grease and Moly Grease should not be done as when they are mixed together they become incompatible with each other.
If you do mix lithium and moly grease together they loose the lubrication properties and can cause your bearings or anything else to wear out much faster.
So only use the correct specified grease in your application and never mix two types of grease together as it will cause more problems and cost you more money in repairs than a tub or tube of the proper grease would cost you.
I once ruined a set of wheel bearings on a trailer during a road trip once by mixing Lithium and Moly grease together and it caused me to be stranded and had to have the wheel bearings replaced on the side of the road which cost me more than it would have if I just bought the correct grease in the first place.