The answer to whether a unit owner has the right to transfer the right to use a garage space as a limited common element will definitely have to be answered by reference to the condominium declaration and/or the association bylaws.  We do this all the time for two reasons.  First, it gives the unit owners flexibility as to how many parking spaces are "reserved" for the exclusive use of a particular unit.  Second, as the value of the use of the limited common elements are usually included with the value of the unit itself, it eliminates having a separate parking space unit with its own tax parcel number (this has been a big problem as the counties in Wisconsin do not index these units separately and it becomes very difficult to search them).

If the declaration and/or bylaws do permit a unit owner to transfer one or more of its parking spaces, it would be very unusual for that transfer to occur by deed -- remember what is being transferred here is the right to the exclusive use of the space, and not the ownership.  Ownership of the common elements is held by all of the unit owners together in an undivided proportional inteterest.

Most often the use rights are transferred by a bill of sale, with notice to the association.  There may also be some approval requirements, maybe a right of first refusal in the association, association fees for the transfer, and other restrictions or obligations.