tramp-connection-properties

tramp-connection-properties is a variable defined in `tramp-cache.el'.
Its value is

nil

Documentation:
List of static connection properties.
Every entry has the form (REGEXP PROPERTY VALUE). The regexp
matches remote file names. It can be nil. PROPERTY is a string,
and VALUE the corresponding value. They are used, if there is no
matching entry for PROPERTY in `tramp-cache-data'.

You can customize this variable.