find and replace, in a proper text editor, because you would visually confirm each change, is absolutely the way to go.
a blanket find and replace is not going to be 100% accurate due to coding styles and stuff;
for example: if you search for CREATE PROCEDURE to repalce it with ALTER PROCEDURE
any differences in whitespace betweent he two words, or where a develoepr wrote CREATE PROC instead;
WITH ENCRYPTION needs to right before the AS keyword, but it depends on coding style, whether you can find 'nAS, or whitespace around it
-- Create Encrypted SP
CREATE PROCEDURE uspEnc
WITH ENCRYPTION
AS
SELECT GETDATE()
Lowell