No. Sorry, just no.

Imagine that you've spent the first 3 weeks of the season developing and training your players and then as you go into the final week of the season your main rival goes on a spending spree in negotiations and buys 11 players @ 119%. What you do? Buy to compete, write the season off or hope for the best?
I think this would turn the season upside down.
I know this is not the real world but imagine Messi wins the league with Barcelona and then is imediatley transferred to Man City to win the league, and then on to Bayern Munich. You can't be allowed to buy such high quality players on the day of a vital league match or a cup final.

Bring back negotiations all season. Restrict to can't sell a player the same season as you bought him.