This app was mentioned in 3 comments, with an average of 1.67 upvotes
Yes you can use the private space for you own, for example the is only in the AppleColorEmoji font, not on other platforms. It shows as an Apple logo in that font.
You can absolutely swap fonts, though some have licence restrictions on them. I made an app that did that on Android years ago, though much better solutions are available now.
Try https://play.google.com/store/apps/details?id=com.quinny898.app.emojiinstaller
A very great app for this sort of thing