I havent got a problem with any player tweaking their game, to say get a better advantage over their opponents, the top players seem to teak their game than others.
I have gone back and watched Coco's matches before she faced Marta
I have noticed that Mata a solid returner put pressure on Coco's serve, then Coco's ball toss suffered and she dropped her racquet head down
Also Coco dosent have to have the speed of her serve soo pumped up, thats when a DF occurs
The serve is always about the 'placement' for starters, going bigger on your serve can bring you undone?
In her game against Saba, well Saba is one of the best returners in the women's games, on both wings, again I felt Coco felt the pressure and her ball toss suffered big time and then the serve resulted in a DF
Before those 2 matches to me Coco and her serve were fine, Coco has always had a problem with her 2nd serve
Coco a hard worker and her team will look back at those 2 matches, and will learn from them.
I also agree it will take a little time for your new ball toss which is vital for your serve, to be 100% but it is all about perseverance.