Why not "Word is God"? Why past tense? Does it mean word was god initially but not anymore?

John says that in the beginning was the Word, and the Word was with God, and the Word was God. Why not "Word is God" - in present tense (because the scriptures are still valid)? It looks like that Word was God initially, but it got changed afterwards and now we cannot say Word is God. When did this change happen? What are reasons responsible for this change? How certain are we that this translation is correct and we are not having the past tense verb "was" due to mistranslation?