How can I adjust the vertical and/or horizontal scaling of text within field scripting?

You can specify the vertical and horizontal scaling of text within an entire field in the field's Format tab. However, sometimes you may need to have part of a scripted field use different scaling than the rest of the text in the field. In this case, you will need to use the transform attribute of a stylerun tag.
The transform attribute is a complicated method of adjusting the scaling, rotation, geometric translation, and skew of text within field scripting. It creates a transformation matrix through specification of six different elements, expressed with numbers and separated by spaces. Fortunately, if you are only adjusting vertical scaling or horizontal scaling, it is fairly straightforward.
<stylerun transform='1 0 0 1.5 0 0'>Your scaled static text or @FieldName@ here</stylerun>
The first element (the 1 in the sample script above) affects horizontal scaling and is expressed in decimal format (0.5 for 50%, 1 for 100%, 1.5 for 150%, etc.). In this example, the horizontal scaling is set to 100% to keep it at the font's original level.
The fourth element (the 1.5 in the sample script above) affects vertical scaling and is expressed in decimal format (0.5 for 50%, 1 for 100%, 1.5 for 150%, etc.). In this example, the vertical scaling is set to 150%.
Note that you must specify all 6 elements but should leave the other four set to 0 to adjust the text scaling only.

More Detailed Information About the Transform Attribute (for Advanced Users)

According to Adobe PDF specifications, the full elements of the transform attribute are as follows:
• Translations are specified as [ 1 0 0 1 tx ty ], where tx and ty are the distances to translate the origin of the coordinate system in the horizontal and vertical dimensions, respectively.
• Scaling is obtained by [ sx 0 0 sy 0 0 ]. This scales the coordinates so that 1 unit in the horizontal and vertical dimensions of the new coordinate system is the same size as sx and sy units, respectively, in the previous coordinate system.
• Rotations are produced by [ cos θ sin θ −sin θ cos θ 0 0 ], which has the effect of rotating the coordinate system axes by an angle θ counterclockwise.
• Skew is specified by [ 1 tan α tan β 1 0 0 ], which skews the x axis by an angle α and the y axis by an angle β.
What this means is that it is not possible to just change one number and understand exactly what effect it will have. It is necessary to start with the effects you want to achieve, including specifying the order, and then do matrix multiplication on them before you can come up with the numbers you'll need in the end.
We recommend that you only use the more advanced features of the transform attribute (i.e. more than just vertical scaling or horizontal scaling) if you are a) skilled with matrix multiplication, b) already know the exact numbers you need, and/or c) have enough time to tweak the different elements to achieve your desired result.