it's possibe to install preview for developers 8.1 + GDR1 without losing Cyan benefits?
Cyan is the firmware. If you already received the OTA Cyan update you will have the firmware and also 'official' 8.1.
PFD is a seperate entity to your firmware and OS. Install PFD and you will be able to get Update 1 without losing what you already have.
Even if you hard reset after installing Update 1, you will still have cyan, 8.1 and Update1...
Enjoy!!!