Biological process

regulation of regulatory T lymphocyte differentiation, regulation of regulatory T-cell differentiation, regulation of regulatory T-lymphocyte differentiation, regulation of suppressor T cell differentiation, regulation of suppressor T lymphocyte differentiation, regulation of suppressor T-cell differentiation, regulation of suppressor T-lymphocyte differentiation

Any process that modulates the frequency, rate or extent of differentiation of regulatory T cells.

regulation of regulatory T cell development

Note that immunologists typically use the word 'development' to refer to cells of B or T cell lineages undergoing the process that GO describes as 'cell differentiation'.