Task Order Conversion to FFP from T&M

We have a task order that is over $10 Million dollars issued under one of our multiple award IDIQ's. Initially it was competed and awarded as a time and material, but as the project has gone on and moved from a design support to a construction phase, we're thinking that converting this to a FFP has some benefits. But now that we've started down that road, we're running into some issues.

I think that I've moved past the need to further justify this award, as it was initially competed, the SOW hasn't changed, and all we are doin is changing the pricing structure. But now that we've moved into this arena, I'm worried that I should be asking for CCAP and requiring competition in my subcontracting. Under the T&M we would approve all of our subcontacts but under the FFP we wouldn't directly approve them. Instead we approve the subK's and pricing when we approve the prime contractors fixed proposed price. Am I overthinking this, or is there something I'm missing? The contract does allow for FFP orders although the majority of them are T&M using fixed rates in the IDIQ schedule, and the contractor is on board with us converting as well. Any help would be appreciated. Thanks.