The 1024-character limit being presented is a product limitation. This means it is the database character limit and there is no workaround at this time. There are other options such as using recipient/sender match patterns in policies, or domain reduction by using wildcards as mentioned in the help documentation.
Release: 16.0 and later
Component: Endpoint
Product Limitation:
In 16.0 RU1 the character limits of the HTTP and HTTPS domain filter text boxes had been increased from 1024 to 4000 characters.