you could do this via an injection but you would not get anything from removing 1 line of code with another one
c.postCode = clientvm.PostCode.postalcode
it's still 1 line
usually injections are done to cover more properties at the same time, sometimes 1-to-1 but if you have the same combination of setting the value
in many different pairs of classes, e.g.
foo.Country = bar.CountryId
foo.Country = jar.CountryId
boo.Country = bar.CountryId etc.
if you have something like this, please show me something like the bigger picture, but if it's just this 1-to-1 property in this single pair of classes, no conventions can be found than it doesn't really makes sense to do an injection for it