As the other answers note, you will need to manually resize the image non-proportionally. The details will depend on exactly what you're trying to do.
Unfortunately your question doesn't seem entirely clear on this — I suspect it's a terminology issue — but what I assume is that you have a 256 × 155 pixel image intended for viewing on a widescreen PAL television display with non-square (1.46:1*) pixels, and you want to scale it so that, after scaling and exporting, it looks the same on a display with square pixels as the original was intended to look on the non-square-pixel display.
If so, the easiest solution is to scale the image width by a factor of 1.46. To do this:
Turn off pixel aspect ratio correction, if enabled. You say you already know how to do that, so I won't need to cover it (or spend time figuring out how to do it myself).
Select Image > Image Size from the menu to open the image size dialog.
Click the chain link icon next to the "Width" and "Height" boxes to turn off aspect ratio lock; now you should be able to change the width of the image without the height also changing.
Set the image width to 146%. (That is, first change the width unit to "Percent" from the drop-down menu, and then enter "146" in the text box.)
Optionally, choose your preferred resampling method, or leave it as the default. (You may want to experiment with this to see which method looks best for your images.) Then click "OK".
Your image should now be scaled from 256 pixels to 256 × 1.46 ≈ 374 pixels wide, and still be 155 pixels tall, and should hopefully look the same on your screen (with square pixels) as it did in the original video.
BTW, not that 374 × 155 pixels is a pretty tiny image by modern display standards, so you might want to scale it up at the same time. While you can do this in two steps, you'll probably get better results by doing the aspect ratio correction and upscaling at the same time. So, for example, instead of scaling the image width by 164% and height by 100%, you could scale the width by 2 × 164% = 328% and height by 200%.
*) You wrote "1:1.46" in your question, but all the sources I've checked say that PAL pixels are wider than they're tall, so it presumably should be 1.46:1. If the pixel aspect ratio for your image actually is 1:1.46, you should scale the image height up by 146% instead.
Ps. While trying to make sure I had the scaling ratio the right way around, I fell into a fairly deep rabbit hole of multiple contradictory sources on what the actual PAL Widescreen pixel aspect ratio is. Some say it's 1.46, some say it's 1.42, and some, like Wikipedia, list both.
Apparently the inconsistency (mostly) comes down to the fact that old analog TV formats have both horizontal and vertical overscan, meaning that the image area normally visible on the screen is smaller, and possibly a different shape, than the full transmitted image — and digital video formats based on the old analog standards inherited this whole complicated mess. So you end up with different screen aspect ratios depending on whether you count the overscan area or not, and while one would think that this shouldn't affect the pixel aspect ratios (which, after all, are supposed to just determine the pixel shape needed to make a circle on the screen look round and not oval), apparently it sometimes does, perhaps due to mistakes in standards or by people interpreting them.
What also particularly confuses me is that, as far as I can tell, the claimed pixel dimensions of your images (256 × 155 px) don't match up with any of the standard PAL video formats, which typically have storage aspect ratios (i.e. width / height in pixels) between 1.22 and 1.25.
Your images, meanwhile, apparently have a storage aspect ratio of 256 / 155 ≈ 1.65, which is actually fairly close to a typical widescreen display aspect ratio of 16:9 ≈ 1.78 or 16:10 = 1.6, assuming that the pixels are square. So perhaps my original assumption is wrong, and you do in fact have a picture with square pixels, and are trying to convert it to a video format with non-square pixels.
Anyway, whatever the case, the general solution is still always the same: use the image size dialog and remember to turn off the aspect ratio lock. Then you'll just need to figure out either the correct scaling ratio (and use "percent" mode) or the actual target pixel size that you want, and scale your image to that. And check that it looks correct afterwards.
