I'll answer your questions one at a time.
I was wondering the same thing. I thought people can highlight your commcode/SIN and check any activities on them but can't you only change your commcode/SIN without changing your commlink like changing a SIM card?
You can easily swap SINs (you can have multiple loaded, in fact, and just broadcast different ones), but what is being traced is the hardware. You can get another commcode, but the rules for that aren't in place, so it requires some GM imagination. Basically, a commcode is your cell number, email, and more. To change all of that takes time, certainly more time than the 15-30 seconds it takes to lift all the illegal data on the commlink itself. You would have to work with your MSP (Matrix Service Provider) to either get a legal change (takes time), or an illegal change (takes money). Either way, you're probably best off throwing the thing away, if it's a burner (1,000 nuyen or less).
I said commcode/SIN because to get a commcode you need a subscription which is registered to your SIN right? And I see the cheap commlink like prepaid cellphone not linked to any SIN.
Commcodes are linked to your commlink. Just like your email and phone numbers aren't linked to your Social Security number, your commcode/commlink is not linked to your SIN. You can load SINs on it (in fact, you have to load them on and broadcast if you want to act legal), but the codes aren't connected to your SIN.
It's been a while since I've read up on the subscription/SIN thing. Looking through
Unwired though, I believe the subscription with your MSP is just a monthly cost. It is included in your lifestyle, but you can purchase one outside of your lifestyle. Most MSPs want a bank account to work with, but some will accept credsticks. Obviously, that means that the ones that only take bank accounts require SINs (real or fake), while the credsticks are completely anonymous.
I mean if the SIN is burnt and the commlink is marked, isn't performing the erase mark matrix action and changing the broadcasted commcode/SIN enough? (may be change the ownership if needed, it's a hard test, but you will not come to stab yourself because you are stealing your own device...)
First, Erase Mark is an Attack action. You cannot perform those unless you are using a deck (in which case, you can easily defend yourself), or you are a Technomancer (you don't even need a commlink). Changing the broadcasted SIN isn't enough, as law enforcement is tracking the commcode/device, not the SIN attached to it. Changing the commcode, if you are completely free of Marks, would probably work. However, this ability was introduced in
Unwired in SR4, and will presumably appear again in
Data Trails in SR5. Since it hasn't come out yet, it's a lot of handwaving by the GM.
Again, using a burner link (1,000 nuyen or less) is just easier. Both as a player, as a GM, and to fit the world of Shadowrun. Paranoia is key, you want to take every step possible to ensure you aren't caught. Erasing information and throwing away the commlink makes it much easier to hide from law enforcement and not be caught.
Also, can you have multiple commcode/SIN linked to the same commlink but only broadcast one SIN at a time and hide/protect/set databomb on the other?
SIN are described as file in the CRB.
You can have one commcode, as far as I know, per commlink.
It is uncertain if you could set up the equivalent of Phone.com or alias phone numbers (numbers that people call that then reroute to your actual phone). A GM could conceivably create rules for it, but I have no idea how it would work with the current Matrix setup.
You can have any number of SINs loaded on your device, but you only broadcast one. Broadcasting multiple is strange and sets off flags. The other SINs are just present on your device in files; you can set them up with databombs, if you truly want. Yes, they are basically files.
The real question is : Do I have to buy one commlink by SIN and throw him if the SIN is burnt or do I only need two or three high rating reusable commmlink and some cheap commlink?
What I advise people to do is to get one commlink at the highest rating you can afford. Use this for data storage, slaving devices for protection, and legal activities. Get 2-4 low-end burner commlinks that you can throwaway without hurting your money supply too much.
You can load your SIN(s) on multiple commlinks. If the SIN is burnt, simply stop using it (and probably delete it, while you're at it). Although, when a SIN gets burnt, you're usually right there for security to advance on you.
If I need one commlink by SIN, how handle ownership? Do I stay the owner of my device whichever commlink I use or is the ownership linked to the SIN or commlink.
You don't need to purchase a commlink by SIN, they are basically just like buying phones. Ownership is a strange thing that's not well defined in the book. Fluff-wise or rules-wise. Basically, this is what you need to know.
If you have ownership status (aka, bought the thing and didn't pick it up off the ground), then you retain ownership, no matter what SIN you are using. Ownership is device specific, so as long as you are the owner of all your commlinks, you will remain the owner, unless someone performs the hardware test or you transfer ownership.
I'm totally lost -_-" (and I didn't tried to figure out how TM handle this)
It's all right, the matrix rules are definitely confusing.
