The limit on select can only be changed by rebuilding the kernel and every other component that uses the select system call.
For the softer limits, make sure that the scripting that runs Asterisk from init is using bash and invoke ulimit before you invoke bash in the same, or a superior shell level.
However note that the defaults are either unlimited, or where it involves pre-allocating the maximum, generous. Also you may find that some limits are configurable, and therefore set, in Asterisk, and I think the stack size for pthreads is determined by that, and not by the kernel.
There are some soft limits set elsewhere, e.g. the temporary file system size, on modern systems, which use RAM and swap, is usually set in /etc/fstab. Other file system sizes are a set by how you partition the disks, further limited by physical constraints.
The only limits I have hit, in practice, is the select one, and that is architectural, so requires the complete distribution to be rebuilt, and physical ones.
Obviously you could also hit limits due to physical resources, like the total disk space.
Linux tends to take a default position that all users are trusted, but other systems may impose default file usage limits, but even then they are unlikely to apply for system daemons started by the system.