If Trump wins a clear majority of the sworn delegates before the convention, they cannot stop him.
See the Goldwater precedent of '64.
What if Trump wins say 40% of delegates, and the rest of field wins 60%. Can the RNC then nominate any one they choose by grouping the 60% for Bush or Walker or Rubio or Christie?
Changes were made to make sure that didn’t happen again. Heck, even the primary delegates can be changed if the GOP doesn’t like the results.
I saw it first hand in Iowa last time Romney lost, but that isn’t the result the GOP wanted to they announced that he won. It took the Paul people at the local caucuses and threats of lawsuits to change that (which was to late for Santorum).
Do you really thing they will let Trump win? The nomination process is not handled the same way as an election.