RB2011UiAS-2HnD-IN antennas

So, I just bought RB2011UiAS-2HnD-IN. The both antennas seem non-detachable, though I’ve read if you open the router you can see they have MMCX connectors inside.

I have external directional antenna (TL-ANT2409A, supposedly 9dB) and been thinking about buying MMCX to RP-SMA connector so I could connect it. I don’t know if this is a good idea, would different antennas causing problems or actually just hurt my signal? what if I buy one more exact same antenna? Or I’m better just leaving the original antennas?

You may have been better buying a connectorised radio such as a Netbox or Netmetal.
I would generally advise leaving the antennas alone on the RB2011