You say "props" so I am assuming the shoes are in pp2 format. Yes  you can apply a MAT pose to both shoes at once. You can just use normal pose file syntax like so:

{

version
        {
        number 3
        }

prop shoeL_1
        {
        material Preview
                {
                textureMap ":MyShoes:lShoe.jpg"
                }
        }

prop shoeR_1
        {
        material Preview
                {
                textureMap ":MyShoes:rShoe.jpg"
                }
        }
}

As Bob said, this will only work once the shoes have been parented to a figure. The shoes do NOT need to use the same material names, and you do NOT need to apply the same texture map to both shoes, though you can if you want. Idealy you should select the figure the shoes are parented to before applying the pose, but it will probably work even if you do not. Note that Poser appends an underscore and number to the end of every prop name. This can cause problems for applying poses to props. For example say you have a figure and you have parented your shoes to it. Now you load a second figure and parent another pair of your shoes to it. The new pair of shoes will be named "shoeL_2" and "shoeR_2". As the pz2 file does not contain any a "shoeL_2" or "shoeR_2" it will not work on this new pair of shoes.

Note that what I have said above applies to props (.pp2). Figures (.cr2) work diffrently to props when it comes to applying poses, so it important to know if your shoes are in pp2 or cr2 format.

Note that you can't list two actors or props on the same line "actor shoeL:1 shoeR:1" won't work.