First early Rodinal contained traces of carbonates from the precipitation of the free base, and it was known Agfa were starting with the Hydrochloride. We won't know exactly what stage, how or for how long they had to do this but at some point the free base was made and purified commercially.
Potassium Sulphite solution has a pH of 9-10 and Calbe RO9 has a concentrate pH of 11.8 which clearly indicates there's not much if any free Hydroxide which is Agfa's claim for Rodinal right from it's early days "Agfa"-Rodinal contains only an alkaline salt of Paramidophenol, but no excess of caustic alkali." So a substitute for R09 should only need enough Hydroxide to form the alkali p-Aminophenolate which will of course affect the pH.
Modern Agfa Rodinal uses an excess of hydroxide so has a pH of 14, a solution of 0.5% alone has a pH of 13 and there is more free Hydroxide than that in the formula which along with the sulphite & alkaline p-Aminophenolate will take the pH to around 14.
I'm not suggesting using Metabisulpite, that was an early method used but requires far more hydroxde to first neutralise it and then form the sulphite, Dr M. Andresen (Agfa) certainly used metabisulphite as the source of Sulphite in some of his formulae, and other contemporaries were doing the same. The major issue is the amount of hydroxide needed will vary depending on the condition and free SO2 content of the powder or solution. This just adds an other unnecessary variable.
It's quite probable that RO9 may need final adjustments prior to bottling at a commercial level. One reason Agfa in West Germany changed the formulae was to make it cheaper & easier to manufacture, by using excess Hydroxide the step needed to balance the p-Aminophenol against the hydroxide has been eliminated and also allows a lower concentration of p-Aminophenol to be used while actually increasing the developer's activity.