I want to buy a 5kW Multiplus-II and I have solar panels with a 6kW inverter (I do reach more than 5kW production). I read that according to the FACTOR 1.0 RULE the inverter of the solar panels should be smaller or with the same power as the battery inverter. Couldn't I do something like in the picture? (I am not sure how I would tell the Victron inverter not to get more than 5kW but If I could, this should work, right?) 
Not sure I understand your question / problem.
You show an PV inverter on the AC IN side of the MultiPlus ==> Factor 1.0 rule does not apply, you can have as many PV inverters on the AC IN side as you want (subject to limitations imposed by your grid provider .......)
Re-read the factor 1.0 rule !
My problem is I want to charge the battery with the solar power generated but I generate +5kW which my inverter is not capable of handling. Is there any way of telling to the Victron inverter when I am generating +5kW of solar just to “grab” 5kW max?
On the AC IN you can have as much PV as you want (and your grid supplier allows).
There is an AC in limit that you can set. It's normally set to about two thirds of capacity, so you need to increase it.
