Yes they change. Diluted developer contains much less sulphite. Sulphite solves back silver an reduces grain and sharpness as well. If you dilute a sulphite-rich dev you get more sharpness and more grain.
By the way, the causality isn´t always as straight as you say. The more you dilute a deveoper, the longer become the development times. Therefore the decreased sulfite has longer time too to solve silver and to reduce the grain. But I read that if the sulfite level falls below some concentration (about 30g per liter) then its solving action decreases strongly.
For instance A49 Tmax 400 (TMY-2) obviously makes an exception to your rule. As I wrote already, I compared A49 at full strength and dilutions 1+1, 1+2 and found no differences in sharpness and grain although I expected it would work grainier and sharper the more I dilute it. In another test I saw that it becomes sharper if you dilute it much more than recommended (1+8). Then it produces coarser grain too. The advantage I got in sharpness was less than the disadvantage in grain. A49 is just no sharpness orientated developer and one can´t change that much. With Microdol-X and Xtol it is probably different.
PS: Please excuse my bad english, but shool is long time ago and I don´t used it about 20 years. To read and understand is not that problem like talking and writing...
Great test, Mr. Beyer! If your interested in comparing with my results regarding TMY-2 in HRX-3 (1+29), Perceptol stock, A49 stock, please look here at post #19:
(there was a url link here which no longer exists)