I copy the plan. RTE 2, so I can change it if I need to. If you switch between RTE 1 and RTE 2, make sure you use Heading Hold (or Heading Select) before you switch them.
Once you switch to RTE 2, LNAV will want to return to the first waypoint of RTE 2, which could be the first one after the SID, so you need to copy the correct waypoint to head to, by copying it to the scratchpad and then paste it to LSK L1 on the LEGS page before switching back to LNAV mode!

Hope this helps