David Vestal in his seminal (at least to me 'The Craft of Photography' - it is what I learned from in my small town library of my youth) talks about manipulating the performance of a Dektol like developer by manipulating dilition, as well as adding stock solitions of potassuim bromide to warm, which I use, and sodium carbonate, which I rarely do, to up the pH and thus increase contrast.

The added carbonate trick I surmise was more valuable when there was a lack of quality MG papers in the market at the time of it's writing. I find it easier to change a half a grade up when a print is a tad too soft in it's base exposure, than to swish up a contrastier developer mix just for that one print.