Is it permissible to avail oneself of the concession (rukhsah) to use pirated software for personal, non-essential use, and does sin result from that, taking into consideration what some scholars have mentioned regarding the permissibility of copying for personal benefit when needed, and when the original copy is unavailable or one is unable to purchase it?

The Gist of the Fatwa (definition):

It is not permissible to copy and use pirated software whose owners stipulate the preservation of their rights, except with their permission. This applies whether the copying is for personal need or for earning money. However, if the copying is for personal need, it is considered less severe. There is no blame on someone who imitates a scholar who deems it permissible, as long as it is not an indulgence in concessions or a following of whims. As for those who follow our opinion on this matter, they must refrain from doing so, especially concerning games and similar items that can be dispensed with.