Need to downgrade iTunes, but need my current library

[Europe calling]

Hi,

I just found out that iOS appstore has silently been removed in iTunes 12.7 (my current version)
I did not miss it earlier, but now i need to dowgrade some apps om my iPhone and i want to replace them with an older version that i keep in my iPhone backup on my Mac (made with a previous version of iTunes that still supported app management)

I know it's possible to downgrade to 12.6.3 but that version cannot read my current iTunes library. And since upgrading to 12.7 a few months have past, my music library has grown a lot, leaving me me with two questions:

1). I know i will not lose songs i added since when i upgrade, but what will happen with all the playlists and changes i have made since leaving iTunes 12.6.3 a few months ago??? Will a need to manually build a completely new library with playlists and all?

2). To avoid the above; Is there another way to acces my iPhone backup on my mac that i made with iTunes, and move individual older apps to my iPhone (not a re-download from the appstore, they only feature current versions)

 

[CoastalOR]

You can manually add the iOS app to iPhone if you already have the old app on your computer (see the "Manually add items from your computer"):
https://support.apple.com/en-us/HT201593

You will probably have to delete the new app from the iPhone before manually adding the old app.