SQL Server Generate Script Between two Checkpoints

SQL Server Generate Script Between two Checkpoints

I'm working on an application that connects to an SQL Server
2005/2008/2012 database.
I have multiple clients, each has his separate database (same schema /
different data).
When developing a new features that require changes to the database, all
DB changes are manually converted into an SQL script that will run on the
client's database in order for him to get the update. Generating such a
script sometimes consume hours or even days when the feature is
complicated.
What I'm thinking of is some tool that can track my changes to the
database between two specified dates or checkpoints, in a way that after I
finish my changes, I take that script and run it on the client's database
and the new application code should be working fine on his end. (Right now
I'm not worried whether the script will contain only Schema or actual data
as well)
Does such a tool exist?