Territory of a halakhic field

Hello Rabbi,
 
I'm having trouble formulating the question, so I'll start with examples:

1. There are poskim (for example, Aruch Shulchan Yod 1999, 39) who permitted the use of large vessels that cannot be immersed.
2. There are some jurists who have permitted, in certain cases, going on a trip to a place where there is no minyan.
3. In several places in the laws of doubt in blessings (for example, the Laws of the Blessing of Fruits, R. Y., 1), Maran does not require one to avoid or change what one wants to eat in order to avoid doubt, but only defines it as a recommendation ("it is good to be careful").

 
Some of the above permissions are based on sources. However, there still seems to be a strong assumption in the background that a halakha on a particular subject is not "permissible" to go beyond its scope and prohibit another subject. Minyan halakha cannot prohibit going on a trip, and birakhot halakha cannot prevent eating in a certain quantity. This is especially clear regarding the immersion of vessels, where I have not seen any anchoring in the sources, but only an assumption.
 
Although there are some general issues in the background that are related to some of the cases (here, here, here, etc.), do you think it is correct to say that there is an opinion, as I wrote, regarding the territorial boundary of a halakhic field?