you should really do this on a dev server and send it for test before you even think about live servers... i assume you have developer or express installed on your own desktop/laptop... why not do it on there first and at least you can unit test it before you think about going any further

HOWEVER you should be able to DROP and CREATE

see the example below which changes the UDT from bigint to int

create proc test as

declare @m dbo.test

set @m=1

GO

/****** Object: UserDefinedDataType [dbo].[test] Script Date: 08/29/2012 09:59:06 ******/

IF EXISTS (SELECT * FROM sys.types st JOIN sys.schemas ss ON st.schema_id = ss.schema_id WHERE st.name = N'test' AND ss.name = N'dbo')

DROP TYPE [dbo].[test]

GO

/****** Object: UserDefinedDataType [dbo].[test] Script Date: 08/29/2012 09:59:06 ******/

CREATE TYPE [dbo].[test] FROM INT NOT NULL

GO