There are several magic items that allow a wizard to add non-wizard spells to their spellbook, such as the Astromancy Archive:
When found, it contains the following spells, which are wizard spells for you while you are attuned to it: augury, divination, find the path, foresight, locate creature, and locate object. It functions as a spellbook for you, with spells encoded on the rings.
Since it functions as a spellbook, per description, it means that a wizard can prepare one (or more) of the listed spells after a long rest.
The problem is that some of those spells are not on the Wizard spell list by default (e.g., Divination): when one searches one of these spell for adding it in the spellbook (under the subpanel Add Spell of the Manage Spell panel), they do not appear, obviously.
Is there any way for a wizard to add a non-wizard spell to their spellbook in D&D Beyond?
Best Answer
Use the spell as a template for a homebrew spell and add Wizard to the available classes.
Navigate to the create a homebrew spell page:
Use the desired spell as a template for a new homebrew spell:
When making a copy of a spell I like to give it a parenthetical note about why I’m making a copy:
Next, add the desired classes to the “available for” section:
And finally, to prevent the copy from showing up on other classes, delete all but Wizard:
Save changes, and the spell should appear in your spell list if your campaign has homebrew turned on:
This is an easy enough way to do it, it took around two minutes to create this spell and write this answer on my iPhone. You might be in for a lot of work if you’re adding a lot of spells, but I could set up the five spells mentioned in the question in less than 10 minutes from my phone, and it would be much faster on desktop.
Homebrew a copy of your subclass.
There is another way to do this, which is to make a homebrew subclass, using your chosen subclass as a template. This method has one notable limitation: it only works with content you actually own, not with content that is shared with you.
If you do own the subclass you are using, you can create a copy of it in the homebrew tool, and there is a section for adding individual spells:
Then it will show up in your arcane traditions section of the class select screen:
And now all of the spells will appear in your spell list on the character sheet. If you add spells that are already Wizard spells, they will show up twice:
Now, I am not sure how changing subclasses would affect other choices you have made, so I would recommend making a copy of your character and experimenting with that one first before making any changes to your live character sheet.