There are several methods for lock disassembly in the field or on a workbench, but almost all of them entail freeing the plug as a critical first step. Ensuring the tumblers are all in their "set" position so that the plug can turn and eject freely can be accomplished in several ways: the pins can be manipulated with pick tools, a bump key could be used, or in rare instances a comb tool can be employed. But all of those tactics leave distinct forensic marks inside of the lock which make these approaches non-surreptitious.
The process of "rear-shimming" with the aid of a factory blank key is the same method used by forensic locksmiths during disassembly of a cylinder, since it does not substantially add new and unexpected toolmarks to the pins or the plug. Naturally, however, this method requires a blank key that is capable of being inserted into the taret lock. For a dedicated field operator, this could mean buying and carrying a very large number of blank keys at all times!
Red Team Tools stocks and makes available a number of "multi-section key blanks" which can be inserted in a wide range of manufacturers' keyways. A key blank like this, along with a cylinder shim (included with this key purchase but also sold separately here on Red Team Tools), can assist you in surreptitious disassembly of a lock cylinder or it can also be used in a pinch in making a copy of a hard-to-source key, it can be helpful during an impressioning attack, or it can even be used to produce a bump key for rare keyways.
This specific key blank is the Corbin GRM (also known as Corbin's "59AD" key) which can be inserted into the AH, FH, BH, DH, C1, C2, D1, and D2 keyways of Corbin/Russwin brand locks.