To find out which type of font you have available, do as Jim suggested, and print a PCL Typeface List from (one or more of) the target printer(s).
How to do this will vary slightly from device to device: many LaserJet printers have front panel menu systems via which such a printout can be initiated (usually via a 'Test' or 'Information' menu).
The printout should show which fonts are available, and should distinguish between 'locations': ROM-resident, DIMM fonts and downloaded soft fonts.
For each font, the list should show a 'skeleton' of the required font selection sequence.
If the indicated sequence shows SPECIFIC 'h' (pitch) AND 'v' (height) values, then the font is a fixed-pitch bitmap font, and is available only in the one size suggested by the given values; I'd expect the 'p' (spacing) value to be 0 (fixed-pitch).
If the sequence shows a SPECIFIC 'v' (height) value, then the font is almost certainly a proportionally-spaced bitmap font, and is again available only in the one size suggested by the given value; I'd expect the 'p' (spacing) value to be 1 (proportionally-spaced).
Otherwise, if the 'h' or 'v' value is represented by a 'placeholder' shaded box, this indicates that the font is scalable:
- if the 'p' (spacing) value is 0 (fixed-pitch), then the list should show that an 'h' (pitch) value (in characters-per-inch units) is appropriate;
- if the 'p' (spacing) value is 1 (proportionally-spaced), then the list should show that a 'v' (height) value (in (1/72 inch) point units) is appropriate.
The font selection sequence ({esc}(9Y{esc}&a124C{esc}(s0p06h09v24700T), which was originally quoted, implies that the font is a bitmap font - and is hence only available in that one size; the {esc}&a124C part is for horizontal cursor-positioning, and nothing to do with font selection.
IF the font IS scalable, then you will be able to select different sizes using 'h' or 'v' values (depending on whether the font is fixed-pitch or proportionally-spaced); any supplied, but non-relevant 'h' or 'v' value (as appropriate) will be stored in the printer's font select table, but otherwise ignored.
You may find that changing the size of a scalable font results in a barcode which is the required width, but is not tall enough; in this case, just repeat the data after adjusting the cursor position to the same horizontal value, but a larger vertical value.
As regards the comment about aspect ratios: you cannot vary the aspect ratio of a PCL5 font.
As webrabbit indicates, you can vary text aspect ratios with PostScript (but then PostScript is quite complex and powerful: more like a procedural programming language).
PCL6 also allows different 'scale' values to be set for vertical and horizontal scaling of text characters; but I wouldn't advise that you think of using this language unless you want to totally rewrite your print application.