Two problems- doubled starter course, and nails.
Normal practice is to double the first course for consistent thickness,
avoiding gaps in coverage, whatever. You're talking adding a course
The existing shingles are nailed down, making it difficult :') to slip
Dunno what you mean by "weaving"- is there a valley?
New courses you're talking will start from bottom (I hope), and you're
hoping that x courses will sync with the existing. Maybe.
Do you want this to look good, or like an obvious cheapie job? The old
shingles will _not_
match the new.
Not being a pro, nor Holiday Inn Express resident, I can see a real
mess, and redo, in the offing. IOW, I'd tear the old off.