\DeclareSourcemap{
\maps[datatype=bibtex]{
\map{
+ \pertype{study}
+ \pertype{position}
+ \pertype{project}
+ \pertype{course}
+ \pertype{thesis}
+ \pertype{committee}
+ \pertype{cvmisc}
\step[fieldsource=date, match=\regexp{\A([0-9]{4}-[0-9]{2}-[0-9]{2})\Z}, replace=\regexp{$1/$1}]
\step[fieldsource=date, match=\regexp{\A([0-9]{4}-[0-9]{2})\Z}, replace=\regexp{$1/$1}]
\step[fieldsource=date, match=\regexp{\A([0-9]{4})\Z}, replace=\regexp{$1/$1}]