It's easy to exceed the allowed transmit power if you do that, so be careful and calculate beforehand.
You can't exceed transmit power with a directional antenna. The radio transmits at a given milliwatt. dBi and dBm are a different measurement you might be referring to.
There's absolutely nothing wrong with concentrating your transmit (send) and receive (listen) with a Yagi or Dish type antenna that covers 700mhz to 2.5ghz.
Sorry, I meant EIRP. A quick Google search says that the limit is 23 dBm for LTE / 5G. With a bigger antenna (= more gain than the standard one) on your LTE or 5G router you'd have to reduce the transmit power (in mW) of the router accordingly, otherwise you'd exceed those 23 dBm.
Is the power limit based on supplied power or “post-concentration” power? I thought it was based on power consumption but I see how the other one would make sense too.