Spells that allowed summons to bolster an other player's/indy province

[HoneyBadger]

That's not bad...the option to improve independent PD might be useful, and would definitely be realistic, since Nations have been doing that all throughout history, and as late as the US aiding Korea, Vietnam, Kuwait, Panama, etc. Places where we don't take over the country, but do send soldiers, money, goods, arms, officers, intelligence, and experience.

Gandalf might be the one to ask about the specifics of how this might work? I think he worked in military logistics.