jren "d{6}(?=.xlsx$)" "ts({fmt:'{mm}{dd}{yy}'})" /i /j

jren "030315(?=.xlsx$)" "ts({fmt:'{mm}{dd}{yy}'})" /i /j

@echo off
setlocal
for /f %%A in ('getTimestamp -f "{w}"') do set "dayOfWeek=%%A"
set "offset=-1"
if %dayOfWeek% equ 1 then set "offset=-3"
for /f %%A in ('getTimestamp -od %offset% -f "{mm}{dd}{yy}"') do set "oldDay=%%A"
call jren "%oldDay%(?=.xlsx$)" "ts({fmt:'{mm}{dd}{yy}'})" /i /j

jren /?

getTimestamp /?

jren /? | more

getTimestamp /? | more