SQL: How to replace an old id with new value

ReplaceOldValue.sql

/*
Assume you have a value in a table that looks like this: 

select foo from bar

|foo       |
|uspFTW 123|

You want to change 123 to 929
*/

declare @newid as varchar(3);
declare @oldid as varchar(3);

set @newid=929 -- this could easily be integrated into a sqlcmd script by replacing 929 with $(newid)

--grab old id (assumes id is on the right most and is only 3 chars long, tailor accordnigly)
select @oldid=right(rtrim(ltrim(foo)),3) from bar

--boom!
select replace(foo, @oldid, @newid) as newFoo, foo as oldFoo from bar