Hi Frazer,
In such case
You will have 2 plans:
1st one will be a Strategy plan with unit WEEK as discussed above (without 10 week package) and the
2nd one will be a single cycle plan with 10 weeks frequency.
Start-of Cycle Dates should be matched.
And then
You need to take help of user-exit IPRM0002 , the logic written there will be skipping the 9 week trigger.
The other option
Can be having a 3 different Single Cycle plans with Cycle periods 3 week, 6 week and 10 weeks with 3 different task lists.
(Hassle free)
Jogeswara Rao K