No, read the PORT, write the LAT.
The LAT holds the last data written to the output latches which may not be the same as actually on the pins. In the case where the low bits are to be written back unchanged the values on those pins are the ones that should be read in directly from the port pins then written back out again. In this particular application it may be that the lower bits are configured for special purposes, in which case it may not matter but the general rule is to read whatever is on the pin then restore it by writing it back.
Brian.