I bought my ticket before April 15th.

They told me I had to fly my first segment as ticketed, otherwise it would force new rules and prices on reticketing.

If the first segment was flown as originally ticketed, then after that I could change anything and grandfather (keep) the pre-april 15th rules.

So the idea conveyed to me was yes you can change flights before you fly your first segment, but it'll force ticket reissue at the post-april 15th rates and rules. So better to change after you fly first segment. Perhaps I was given wrong info, just passing along what I was told.