Any process that modulates the frequency, rate, or extent of metaxylem development. Metaxylem development is the process whose specific outcome is the progression of the metaxylem over time, from its formation to the mature structure. The metaxylem is the part of the primary xylem that differentiates after the protoxylem and before the secondary xylem, if any of the latter is formed.
regulation of metaxylem development