No, big mistake. You do not want to dilute his GOP vote, which he will have as the nominee, with a write in.
You are correct, if Trump is able to out-maneuver the GOP-e dirty tricks that they are now ramping up in every state possible, as they manipulate dynamics.
However, just in case, we should have a strong presence telling the GOP-e that this is the last time we will vote for any Republican-e toadie that will continue to stab us in the back.
If this will be the case, the GOP-e needs to go down, and I will be happy to contribute by voting 3rd party......write-in....if necessary.
If they treat us unfairly, we will have a tool.