The sockets are the same, you would ahve to contact MSI and Asus is the BIOS supports them but I wont see any issues are they are very closely related. All that being said ttaking apart a laptop is difficult and if you have never done I before I would not recommend it. Some manufacturers solder in the CPU's while it is not as common as it used to be if the CPU is soldered in than you cant remove it.
I have an ASUS U50F and would be interested in the result of your effort to upgrade it to an i5. I assume if it worked there is a bigger drain on the battery. I have thought of upgrading my battery to one with more cells as the battery life is less than I would like for his laptop.