Resepected Riot,
Please Allow Mid-Season Trading between the franchise teams.
Your's Faithfully
UFC
It's not possible to have mid-season trading. Among probably a bunch of other reasons, fledgling teams would be frantically taking the best players from the challengers teams which would make both the Tier 1 scene (with no guarantee their new teams would work) and the T2 scene (which would have teams that to restructure mid-season) insanely unstable.
In short, currently, teams are being incentivized to make good decisions at the beginning of the split and they have the opportunity to sign up to 10 players if they anticipate they're going to have roster issues.