Magic items and runes

[Draven Torakhan]

In this case specifically, a Bloodlettung Kukri. It's a +1 Striking kukri, but it has an additional power.

My player has some downtime and wants to know if they can get another rune added, if they need to increase it to a +2 first, or of it's even possible.

[NorrKnekten]

They can freely upgrade or move around the runes already on it, But it cannot gain any property runes.

Source GM Core pg. 241 2.0 Specific Magic Weapons wrote:

These weapons have abilities far different from what can be gained by simply etching runes. A specific magic weapon lists its fundamental runes, which you can upgrade, add, or transfer as normal. You can’t etch or transfer any property runes onto a specific weapon that it doesn’t already have, and you can’t remove its property runes.

[Draven Torakhan]

Appreciate the help, thanks~