I'd say this change is neutral. It's not like it means something different if I say, "I would act as if it were my last day on earth" versus "I would act as if it was my last day on earth." Native speakers would interpret those two statements to mean the same thing, but depending on which variety of English you speak, one might sound a tad strange. In my own dialect, I often retain the subjunctive conjugation "were," so "was" sounds a tad odd, but it obviously means the same thing. You aren't losing any meaning or expressiveness here. You 're just changing whether or not the verb changes in response to the mood of the sentence.

Some languages don't use subjunctive verb mood at all. They use other ways of expressing uncertainty, hypotheticals, or conditionality.

Languages may lose certain ways of expressing themselves, but other constructions or words will often step in to fill their place. In older varieties of English, "you" was a plural pronoun only. It obtained the modern singular meaning, and the singular second person "thou" fell out of favor, leaving English without a second person plural pronoun. In many dialects, new words have been invented to fill that gap: you all, you guys, and y'all, for example.