Changing the Channel Bandwidth on GNURadio


Hello guys
So, I have this doubt that I am trying to solve which is basically the following:

I was reading the tutorial for beginners on LimeSDR with GNURadio, trying to know how can I change the channel bandwidth of my application.
Let’s suppose I’m working with a baseband technology and that I need a bandwidth channel of 1.25 MHz, but that technology doesn’t channelize in 1.25 MHz (Zigbee for instance). So I use the LimeSDR to solve that problem adjusting the BW to 1.25 MHz. But how can I do that (changing the channel BW) on GNURadio’s Lime blocks that I’m working? I also read that the minimal BW that I can use on GNURadio blocks is 2.5 MHz, is that correct?