Rename all stored procedures in SQL in a single query

You can dump a script to do all of this and then just run the script

select STRING_AGG(CAST(
    'exec sp_rename @objname = N' + QUOTENAME(s.name + '.' + p.name, '''') + ', @newname = N' + QUOTENAME(LOWER(STUFF(p.name, 1, 3, 'proc_')), '''') + ', @objtype = ''OBJECT'';'
    AS nvarchar(max)), '
')
from sys.procedures p
join sys.schemas s on s.schema_id = p.schema_id
where p.name like 'sp[_]%';

You can even put that into a variable and run it through sp_executesql if you are that (fool-)hardy.