If it is for adding information regarding deceased persons and they have a normal FamilySearch account, they (and ANYONE else with a FamilySearch account) can already do this. The FamilySearch FamilyTree is a single tree owned by FS that is SHARED by everyone.
For records that you have entered for living individuals, in general you cannot share those. However, members of the church with FS accounts can assist you using the "helper" capability in the system. In this case I believe that they can see and modify your LIVE persons. But giving someone your ID and password for your FS account is usually not a good idea.