Can and aircraft limit be broken for SAR?
NO.
It's really quite simple. The rules must be followed. Whenever a crew operates outside the rules, they may be subject to the consequences. With valid reasons to operate there, I'd hope that the consequences would be the exception.
One of the mistakes that is frequently made is the crew isolates themselves. Instead of being a part of a National SAR response, they become, in their mind, the only resource. If your rules, crew or machine is not capable of completing the mission, then perhaps there is another resource that can.
Once you determine that there is no resource, then the outcome of repenting must be compared to the outcome of pressing. Sometimes your best efforts are still not enough. If that's obvious early on, then don't break rules.
You now deem that there is a good reason to operate outside your rules (risk analysis) and there is no other resource to complete the mission. Now is the time to confirm your crew agrees with your plan, and if so execute it.
Sometimes all of the above happens in seconds, sometimes it can happen whilst flight planning on the ground.
I can give examples of exceeding parameters to save lives, exceeding parameters for no good reason, turning down missions that could have been completed by exceeding parameters (some with fatal outcomes), etc. In all but one of the examples, neither I, my peers, nor my superiors found fault in the decisions. In the one exception only a debriefing occurred.
The crews should never feel pressured to go beyond. When a National SAR system is designed, the limitations of the resources would have been considered. A high percentage of mission completion will be a part of the plan, but it won't be 100%.
Time to sum up. SAR crews don't have blanket authority to break rules. If they choose to they must consider other resources, risk analysis, the crew, the machine, and the rules. They mustn't feel pressured to provide what their country has chosen not to provide. All that being said, I think the best way of summing this up comes from our orders:
A too literal interpretation of these orders, that negatively affects the provision of SAR services, was never intended.