Interesting, the conventional wisdom in the 80's and 90's (in the UK) was that the best way to alter the curve with Rodinal was by altering it's dilution, and that works extremely well.

Peter Goldfield was the Guru of Rodinal, the quality of his 35mm Agfapan negatives and prints was stunning, many wouldn't believe he'd shot them with a Leica and not medium format. Peter had gone on workshops with Paul Hill before spending some time with Paul Caponigro in New Mexico, he imported Agfa materials into teh UK, rebuilding their market, and was a staunch supporter of the workshop system.

So there's another approach which is fairly unique amongst developers for controlling the curve. I used 3 different dilutions for N+2, N and N-2 development which gave far more control than simply altering development time or agitation.

Ian