What improvements are you thinking?
I see three avenues:
1) Clothing - Already banned in the Olympics
2) Medication - Also officially banned in the Olympics but the Enhanced Games look like a promising test bed.
3) Go full Cult Mechanicum?
growing your body optimized for swimming. The training is one thing. I mean shaping your body into the hydrodynamically optimized form, like say growing some muscles (or fat - shaping yourself into a more dolhpin like shape :) here and there mostly for the purpose of better resulting hydrodynamic shape. With the medicine advances it may start earlier in life and be non-catchable by the sports authorities.
And, if you look at one of the Chinese Olympic winners last year - the wave in front of him was significantly smaller than in front of anybody else. Have no idea how he achieved that though.
I was thinking of optimized movement patterns to increase efficiency / reduce wasted energy. This numberphile video explains how fish and other swimming animals barely lose any energy, even though they create vortices, because the vortices are in turn used to propel the fish forward.
https://youtu.be/wYDh5d9pfu8?si=TkPs2xcngduz_Qem&t=600