Disclaimer: This article is for educational and historical purposes. Download and use abandonware at your own risk. Always support software developers when possible.

Duplicate layer → apply Gaussian Blur (0.5–1px) → use Layer Style > Blend If to restrict blur only to shadow/midtone noise.

However, I can offer you a article outline that respects copyright while still helping users achieve similar "grain surgery" effects in older versions of Photoshop (including 7.0) using legal means:

Grain Surgery was a renowned Photoshop plugin originally developed by Visual Infinity

While the software is dead, copyright law usually persists. Downloading cracked or unauthorized versions of software remains illegal in many jurisdictions, even if the original company has dissolved. While the risk of prosecution for a 20-year-old plugin is low, it is a factor users should be aware of.