KJV
Isa 46:10
Declaring (מַגִּיד ,MaGGiYD , hiphil participle)
the end (אַחֲרִית , 'aHaRiYT) from
the beginning (מֵרֵאשִׁית , MeRe'ShiYTH) , and from ancient times (וּמִקֶּדֶם , W-MiQeDeM , from the east)
the things that are not yet done (אֲשֶׁר נַעֲשׂוּ, aSheR Na'aShU, Piel perfective pl.), saying, My counsel shall stand (תָקוּם , ThaQUM, Qal imperfective, is standing/will stand), and I will do (אֶעֱשֶׂה, "e'eSheH, Qal imperfective, I am doing/I will do) all my pleasure:
Isa 46:11
Calling a ravenous bird from the east, the man (אִישׁ , 'iYSh, indefinite)
that executeth my counsel (עֲצָתִי , 'eTsaThiY, Noun fem. construct, of my counsel) from a far country: yea, I have spoken (piel perfective)
it, I am/will also bringing/bring it to pass (hiphil imperfctive); I have purposed (qal perfective)
it, I am/will also doing/do it (Qal imperfective) .
It's easy to manufacture doctrine by wresting verses out of context and finding a translation that sound like it presents your presuppositions.
The underlined nouns that the KJV and NIV translate as definite, are in fact indefinite. The word translated as from ancient times isa word most often meaning east, which makes perfect sense here, since the attack is coming from the east, so why use "from ancient times" instead? So more accurately, YaHWeH is saying,
"[I am God ('eL) I am God ('LoHiYM)] declaring an end from a beginning, and from the east things which are not
yet done. saying, "My counsel is standing/shall stand, and I will do all my pleasure; calling a ravenous bird from the east, a man of my counsel from a far country: yea, I have spoken
it, I am also bringing it to pass; I have purposed
it, I am also doing it.
So, the context is not a general statement of God declaring everything from the beginning of time, but God declaring a new beginning to a plan which He will accomplish, to bring a man of His counsel from the east, who is as a ravenous bird towards Israel. And God is expressing His present determination to bring it to pass. As with all God's prophecies of punishment, they can be rescinded if the person or nation threatened repents. So God is presently putting His plan into action, but He could possibly defer it, if the nation repents, since He responds with mercy to the contrite.