Answer by AlexS

You can also do this with plain T-SQL:

DECLARE @sql nvarchar(max)

DECLARE c CURSOR FOR
SELECT [definition] FROM sys.sql_modules

OPEN c
FETCH NEXT FROM c INTO @sql
WHILE @@FETCH_STATUS = 0 BEGIN
    SET @sql = REPLACE(@sql, '<Your search string here>', 'Your replacement here')
    SET @sql = REPLACE(@sql, 'CREATE PROCEDURE', 'ALTER PROCEDURE')
    EXEC sp_executesql @sql
    FETCH NEXT FROM c INTO @sql
END
CLOSE c
DEALLOCATE c

Be warned, however, that if you ever used sp_rename to change the name of SP, you're in trouble, since sp_rename does not update SP name in sys.sql_modules so you'll get an old name after all (as totally valid pointed by James Moore).