Using Stored Procedures To Set The Default Value Or Binding Of A Table Column

I want to be able to have an authorized person set or change the default values of a table column in a SQL Database. I have a stored procedure that sets the default which works fine: ALTER PROCEDURE [dbo].[addMyConst]
AS
BEGIN
ALTER TABLE [dbo].[tbl1]
ADD DEFAULT 70 FOR [Auto_ourlim]
END

(I still need to put parameters in so that I can run the stored procedure from a form, but for now....)


 To change it I know that I have to drop the constraint first like this:

ALTER PROCEDURE [dbo].[dropmyValue]
AS
ALTER TABLE [dbo].[tbl1]
DROP CONSTRAINT [Auto_ourlim] 

The problem is that when I execute the procedure I get the error that "Auto_ourlim" is not a constraint so it does not drop the Default Value. When I go over to SQL Server Management Studio Express I can see why:

If I open up the table and open up the Constraints the constraint is "DF__tbl1__Auto_ourli__5FB337D6". I could change the DROP CONSTRAINT to this, and that works, but it changes every time I add the new DEFAULT VALUE.  I don't know how to get around it. Is there a way to put wildcards around "Auto_our" in DROP CONSTRAINT [Auto_ourlim}? Any suggestions would be welcome...even if there's a totally different way to do it.

What I'm trying to ultimately accomplish is this: Column1 (AutoLimits) would be user insert to the database and then in the database it would MINUS Column2 (Auto_ourlim - set with the default value) = Column3 (Difference - a computed field in the database)

Steve