Full synthetic to synthetic blend
 

When i bought my GS350 08 at 105k miles, lexus dealership had put a high mileage synthetic blend

Since then i have changed engine oil at 110k and 120k with M1 Full synthetic

From my understanding there is no harm going from blend to full, but is there any complications going other way around?

No complications.

Correct, switch back and forth at any time (or mix even)