From the author's README on Thunderstore

This mod adds:

1 Holographic Half Life Logo Deck
1 Half Life Logo Griptape
3 shirts
- White Tee Graphic with Big Half Life Logo
- Black Tee Small Half Life Logo
- Black Tee Big Half Life Logo
1 Black Longsleeve Big Half Life Logos
1 Black Hoodie Graphic with Small Half Life Logo

Installation

Open the ReSkate Launcher and go to MODS.
Search Half Life Cosmetics and click Install.
Press PLAY and find the items in the customization menu

Notes

Made with ReSkate Studio.
Unofficial fan-made pack, not affiliated with or endorsed by Valve. All designs belong to their respective owners.

Install Half Life Cosmetics

You need ReSkate and your own copy of skate. on Steam.

Open ReSkateLauncher.exe and go to MODS.
Search for Half Life Cosmetics and click install. The launcher also installs anything it depends on.
Press PLAY. In game, the MODS tab of the ReSkate menu (Insert) turns it on and off.

Or install it by hand: download the .zip and drop it on the launcher window, or unzip it into its own folder in Mods\ beside Skate.exe.

Maps show up in the ReSkate menu's level list. To join a server running a custom map, you need the same map installed. If the game won't load after installing, see known issues.

skatemods doesn't host or review this mod. The download comes straight from Thunderstore. Only install mods you trust, because scripts can run code.