Hello! Is there anything like API for manipulating SwOs configuration? I've looked at the protocol, it seems quite easy to use (e.g. POST /links.b with some json data can tune ports). But before going to reverse engineer and implement those POSTs I'd like to check if there is any existing framework for that.

no, there is no documentation or API to control SwOS devices. You can look for CRS2XX series devices that will have all the usual RouterOS management features allowing to configure switch that way.