Unable to add mods to inventory

[BSonPosh]

Problem

The mods system isn't fully baked yet. This is a known issue.

Work around

Create a new custom item with the attributes of the modifications. The GM should still go through the enhancement and modification process with the player.

Example

Player wants to add Accuracy Focus Mk III to their blaster. The GM would go through the process and if successful the GM would create a new weapon item with a +2 bonus to attack rolls.

[Ikaguia]

With the move to dnd5e 4.0.0, the 'modification' item type is no longer needed, since dnd5e has the 'enchantment' system.
In your example, the 'modification' item would be a regular item, with an enchantment that gives a +2 to attack rolls, the player would just need to import that item, use it and apply the enchantment to their item.

Enchantments are much more versatile than the old modification items, and much less buggy, they are basically active effects for items. The only feature lost in this transition is the counter of how many modifications/augments you can have.

(there is no pre configured modification with enchantments yet tho)

[Roymitch]

I struggled a bit with this, but I eventually got things to work pretty nicely for myself and want to pass along what I had done to give others some idea. I am unsure if it is the cleanest way or best practice, but it worked for me.

Remaking older modifications as equipment with the enchantment action type allows for really clean modification. The only thing it misses out on is a count of modification slots used, which I consider pretty minimal.

Notes on enchantment basics are found on the DND5e wiki here.

I will use the darkvision visor as my example. For it, I created a piece of equipment with the normal description.

Then under "Details" I went straight to the "Equipment Action" and set it to enchant and went to configure Enchantment. On the next screen, I selected "Create Enchantment". This then opens the active effect panel for it.

For me, I set the enchantment to force the target to be marked as requiring attunement, set it to enhanced and added the modification to the item's description.

That alone is enough for most items where you are only modifying the item's abilities, but the darkvision visor needs to affect the actor (and token) as well, so there is one more part. For this, you will need to navigate to the "Effects" tab of the modification. In this case, we need to add a "Passive Effect" to the item as well. This will be the one that applies to the actor who has the modified item equipped.

This effect I set with mixed priority values, as the darkvision visor affects people without darkvision differently than people with darkvision. First priority 19 processes, which adds 30ft to the vision range for both their system attribute and their token's vision range (requires Active Token Effects for all attributes that start ATL.). This is to cover characters who already have darkvision. Then on the second priority 20 I set their token's vision to darkvision view and then upgrade the tokens vision to 60 feet if it is lower. So any user without darkvision would have been set to 30 then 60, but a token who started at 60ft darkvision would be increased to 90ft.

With those settings in place, your Effects tab should look like this:

Go back to the Equipment Action setting from earlier and configure the enchantment once again. This time you will need to look in the "Additional Settings" dropdown for the enchantment to add the additional effect which we made earlier.

Now the modification is complete. If I apply it to a piece of armor it changes all the settings I requested.

(Note the text for the modification)

After all this fiddling around, I only have a few notes:

1. This approach does not have a built-in way to tell how many modifications an item allows, rarity restrictions, or any restrictions on what specific items they can apply to (Might be different in DND5e 4.0). It also does not set that modified items require attunement unless you apply it like I had above. It feels like a bit of a workaround to me, but it definitely works.
2. Even though the modification type is not strictly required, I wish I could at least mark their equipment type as "Modification" instead of leaving it blank or maybe marking them as trinkets. Anything that allows me to show them separate from other equipment in the inventory.
3. I wish I could include an installation check when attempting to apply the modification, but this appears to be a limitation from DND5e.

Hope any of the above helps!