It doesn't seem to me they're talking about "changing" the rule so much as enforcing it. As I read this, unless someone had won an outright majority in 8 states, then there's not a first ballot nomination. ALL the names are in play, and they just call the roll for each state until someone has a majority of delegates.
https://s3.amazonaws.com/prod-static-ngop-pbl/docs/Rules_of_the_Republican+Party_FINAL_S14090314.pdf
And more clearly
RNC convention first ballot rules for candidates who fail to pass rule 40b?
But, if the Donald goes into the convention with 1272 pledged delegates, and is NOT the nominee, then I think the gop's in trouble.
If a candidate does not meet their requirements of the 40B rule, then any delegates pledged to them will be ignored on the first ballot. All delegates are released after the first ballot. So the second part you speak of its erroneous. There will be a nominee, as that is the whole point to the convention.
But who can be eligible for the nomination of the Whole convention currently requires a delegate majority in at least 8 individual states. That will only Trump and maybe Cruz.
By changing rule 40B, anyone that has won a single delegate can be put up for nomination, even winless Jeb!
So the way it would have worked under current rules is....
If there is a candidate with a majority of ALL delegates, then they win the nomination outright.
If not, but only one qualifies under rule 40B, then, as I understand it, there is a first round vote for only the one candidate, he does not get a majority since all delegates are still bound, even if their vote is not recognized. In the second round and following, only the one candidate that met the conditions of rule 40B can be put up for the vote, and that candidate would win by default.
If two candidates qualified under rule 40B, then there is the symbolic first round of winless voting, then starting in the second round and following, the only candidates that can be considered are the tow who met the qualifications of rule 40B. Only one of them can possibly win the nomination.
The point of changing the rule is to allow other candidates to be considered even if they have only one delegate. This means that if a majority is not found the first round, in the second and following rounds the delegates can horse trade until they finally get a nominee and that could be anyone from a loser like Jeb! to Trump.
Right now only Trump and Cruz are likely to meet the qualifications of rule 40B, certainly Trump sill get it and quite possibly Cruz. They have an advantage that they have worked hard for in that they have won majorities of state delegations and to change the rules prior to this convention is to defraud them of their fairly gained advantage in the nomination process.