Hello,
Yes this is permissible. The data sheet allows for a MCLK period as short as 37 nS in 512 x fs mode. This corresponds to MCLK as high as 27 MHz, or a sample rate of 52.7 KHz. Thus, 51200 is fine.
You can have SigmaStudio compute filter coefficients for your new sample rate by right-clicking your input cell and entering the rate:
Best regards,
Bob