Runtime topics remapping ?!

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so, if i had 100 robots (nodes) and each of those had to communicate with just ONE (among all robots) and this "one" changes over time, i should write 100 subscriber/publisher declarations!?!?!

Well, you will have 100 total. For each robot, however, you would only have one declaration. If the ONE to connect to changes, you will just change what this single declaration points to in each robot/node. In the simplest form, you'd move the subscribe/advertise call from the init code.

thanks, i know this solution but in this way my system would be extremely inefficient in terms of scalability...(i should modify the code every time the number of robots changes).

No, that should not be necessary. Can you maybe update your original post and give some more explicit use cases what you'd like to happen, e.g. something like: robots/nodes and topic connections before - something changes - robots/nodes + topics after. This can probably be done without code changes.

As to scalability: If you want to connect 100 robots to one and then change to connect to another one, you'd have to change those 100 connections physically. Besides that there should be no overhead.