There is a preference setting that allows you to make the salinity in the 'Information' tab adjustable even for dives downloaded from a dive computer:

But note that if you change this setting the rest of the data reported by the dive computer, like NDL or TTS will be unaffected, meaning that the data in your dive profile becomes inconsistent.
Ngā mihi
Michael Keller
-- GCS$/CC/E/IT d- s+ a C++ UL+++/S++ P L++ E-
W++ N o? K? w O(++) M-- V+ PS+ PE+ Y? PGP+ t
5? X R tv b++ DI++ D++ G e+++ h---- r+++ y+++