I customized paths and my progression looks like this: Rycerz -> Paladyn

utility:
    inherit: default
    extra_spells:
      - push
(...) much more spells

rycerz:
    inherit: utility
    name: Rycerz
    upgrade: paladyn
    upgrade_item: paladyn_upgrade
    spells:
      - dash
(...) much more spells

paladyn:
    inherit: rycerz
    name: Paladyn
    max_mana_regeneration: 6
    mana_regeneration: 5
    mana_max: 125
    mana: 125
    spells:
      - railgun
(...) much more spells

This is my upgrade item:

paladyn_upgrade:
    icon: gold_sword:1 # does not apply
    upgrade: true
    hidden: true
    hotbar_count: 3

The thing is after buying all needed spell and upgrade, hotbar_count:3 is applied, but icon not, also wanted to change Name and Description, but they're not applied either.

MC Version: Spigot 1.13.2
Magic Version: Magic-7.6.17

Do you plan to extend reference with their properties?

Possibly, but not sure. Haven't had much time to spend on this in general lately!

And one more question, a bit less related with item upgrade. Can I somehow send commands when UpgradePath is succesful?

Yes, you can- these are used in the default configs to broadcast path upgrades:

https://github.com/elBukkit/MagicPlugin/blob/master/Magic/src/main/resources/defaults/paths/default.yml#L7

So on each path you can override this- you'll need to keep the broadcast in each path if you still want it. Like:

paladyn:
 upgrade_commands:
    - broadcast &6@pd &3has advanced to &b$path&3!
    - perm user @p group add paladyn

That's awesome. Thank you, keep up great work :)

Since upgrades are actually items they have their own icon/name/description that they use, and you don't always want those to transfer to the item being upgraded. So there are 3 special properties for when you do:

paladyn_upgrade:
  upgrade_icon: gold_sword:1
  upgrade_name: Paladyn Wand
  upgrade_description: It is super awesome

Great! upgrade_icon does the work.
Unfortunately upgrade_name and upgrade_description does not override the wand's name and description.

Are these properties documented anywhere? I couldn't find items/paths properties at http://mine.elmakers.com/reference

Wand properties are here: http://mine.elmakers.com/reference/#wands

But the upgrade properties aren't listed. There is no reference for paths.

I think you may need to add force: true to get the upgrade to change name and description. This makes it force-apply all of its settings, which could be a problem if players are allowed to have more than 3 hotbars (through other means, shops, etc) but otherwise should work fine.

Yes, force fixed it. Thank you very much!
Do you plan to extend reference with their properties?

And one more question, a bit less related with item upgrade. Can I somehow send commands when UpgradePath is succesful?