You can, but you'll have to deal with the consequences of violating conventions and the impact of that might matter very little or a whole lot depending on the

You can, but you'll have to deal with the consequences of violating conventions and the impact of that might matter very little or a whole lot depending on the situation. Running a random service over port 80 can be a good idea (lots of networks have that port open), but you'd better be willing to deal with the traffic from people/bots/crawlers looking for a webserver there. If you aren't careful you can break things on your own network or get yourself cut off from others. The rules and standards that exist are there to make everyone's lives easier and promote things working. Deviate from them at your own risk.