Deviations from PCB reference design

[meshs]

I'm basing my PCB design on Nordic's reference layout. The product I'm developing will only be used for research, and is basically a one-off design. How closely do I have to position the components with regard to the reference design to end up with a product that functions? More specifically, referring to the reference layout attached: would it still function if e.g. C13 and C14 were moved north by ~5mm? Are there any components that should absolutely not be moved, such as the antenna specific parts?

[ketiljo]

As a general rule, leave the RF part (matching network) as in the reference layout unless you have a very good reason for it. Any excessive track length here will have negative impact on the radio performance. 

Decoupling capacitors should be placed relatively close to the pins. 

When it comes to C13 and C14, they are only needed to lower the LO leakage by a few db and will not have any practical impact on the functionality of the design. So unless you plan to have it approved in Europe, you can remove them.

[meshs]

That is great news! Somewhat related: I'm considering 5 GND vias (same dimension as ref design) as opposed to the eight in the ref design. I also consider leaving them open (not tented), at least on the upper signal layer. Do you think this will be an issue either during soldering or for the functioning of the device? I realize it is probably hard to give an exact answer to this question, but an educated guess is good enough. I it is not like I would hold Nordic responsible in case it turns out not to work :-)