My question is:

Is there any instruction in RSLogix 5K that can allow us to examine a tag name so that the results can be used to form a set of conditions to activate an output?

In fact, I need to write a program code for the following:

Fetch tag name (eg: M03XV003) corresponding to the generic name (GFEED).
Parse out the left-most character of the tag name.
Test to see whether left-most character is an 'M'.
If character is 'M'.......

and so on.

My problem is that I do not know whether it's possible to write these above instructions in RSLogix5K.....have you any idea on how this can be achieved?

I dont know of any instructions that would allow you to examine the tagname. I also cant think of any reason that I would need to do that. Maybe it would better to back up and talk about what you are trying to achieve. There is probably a way to do what you want to do just maybe not using tag names. Indirect addressing, data structures, etc may allow for different methods to achieve the end result you want. For example you may be able to make a data structure that contains elements that would allow you to do the tests you are interested in. Post some more information and maybe we can come up with a solution.