YouTube allows for certain levels of customization when it comes to the subscribe button. For instance, you can add a watermark, which could be a logo or any other icon, including a custom-made subscribe button, that appears in the bottom right corner of your video. You can decide the timing of this watermark - whether you want it to appear throughout the video, at a certain time, or towards the end.
However, the actual subscribe button that appears below your video alongside your channel name can't be customized as it is a fixed design element from YouTube. This uniformity helps maintain familiarity and recognition across the platform. But with creative use of annotations, graphics, and verbal requests, you can effectively draw attention to the subscribe button.