Let me see if I understand correctly;
(1) Animal rights activists are trespassing on a farm. I am assuming this farm has all nessesary permissions / registrations etc.
(2) The activists are placing noisy electric and / or mechanical devices on the roof tops of the housing units used by the farm owners and / or workers, denying them sleep and therby reducing their eficiency and interfering with legal trade and commerce.
(3) The activists publish proof or admissions of guilt on the web.
If so, your plan to increase the legitimate destruction of pests and to let them know about it sounds good to me (important: I am not a legal expert).
Here are two more thoughts on the matter. I wonder if they are equally as good or at least useable?
(a) Provide to the doorstep of these activists free samples of the best edible game you can harvest, whether they want it or not. Insure it is properly cleaned, well packaged, and include a recipe. I assume that the police will not view trespassing on their apartment units or whatever housing they use as any more serious than their trspassing on the farms?
(b) Investigate the use of trade agreements: example: if any of these activists are from other countries or affiliated with such, Could the European equivalent of "free trade" laws be invoked? example: casting their activity as illegal disruption of commerce in one country by forces from another country?
In closing: My perceptions of Sweden may not be very accurate or up to date but I've percieved Sweden as a socially progressive land of reasonable firearms laws and with good outdoors sports traditions. My best rifle comes from Sweden and bears the crown of your king. I am saddened to hear that your traditions and culture are being attacked.
BB