According to our existing documentation:
How to Modify Schema Using Web Screen Painter - CA Service Management - 17.1 - CA Technologies Documentation
You cannot use WSP to change the length of an existing column, and we strongly recommend that you do not use other tools to do so. Changes to the length of an existing column are not supported, and may cause other applications accessing the CA SDM database to fail.
The reason for this is that Service Desk assumes a baseline schema design that is common across implementations. Any patches introduced that could modify the schema may roll back or even cause unexpected results if such a change was introduced to a given field defined by the Service Desk initial install.
A common approach to work around this is to create a separate field whose size would accommodate for your requirements, and have the original field hidden from access.
Another thing to keep in mind is that SQL Server does have a limit to row length as well.
SQL Server 2016 Maximum Bytes/Row - Database Administrators Stack Exchange