I want to mod the Viking Age start so that rather than Ivar the Boneless invading East Anglia, it is Guthrum/ Guttorm (the viking who historically became king of East Anglia) who is doing so. Since he is not a landed character I think the best way to achieve this is by making him an adventurer who is using an adventurer conquest type cassus belli.

How would I go about doing this?

I think I will need to create an adventurer hoard title for him to be leader of. Whilst I know how to mod titles, and create new normal titles I do not know how to make an unusual title such as this.
I would then need to give him troops and possibly boats - again, I don't know how.
Then I'd need to put him, and his troops/ boats in a suitable location.
Then I would need to make a new war history, or more likely, modify the existing viking invasion one, including changing the cassus belli.
Please can someone advise on how to achieve all this. As I say, I have some experience modding, and I feel like this should be achievable, but I don't know how.

Many thanks