From CS:GO

Put the v_*.mdl, p_*.mdl, and w_*.mdl files into your cstrike/models folder. If the files are named v_knife_w.mdl, p_knife_w.mdl, and w_knife_w.mdl, rename them to v_knife.mdl, p_knife.mdl, and w_knife.mdl respectively, or replace the existing files with the same names. Back up the original files first. Custom sounds go to cstrike/sound following the original folder structure.

Put v_knife_w.mdl and p_knife_w.mdl in the cstrike/models folder. To make the game use them, rename them to v_knife.mdl and p_knife.mdl (or replace the existing files with those names). The w_knife_w.mdl file also goes there and should be renamed to w_knife.mdl.

If CS 1.6 crashes or the knife model does not appear, check that the model files are in cstrike/models and correctly named. Ensure you did not mix up v_, p_, and w_ files. Also verify that the model is compatible with your CS 1.6 version. Restore your backup if needed.

To revert to the default knife, delete the custom v_knife.mdl, p_knife.mdl, and w_knife.mdl from cstrike/models and restore the original files from your backup. If you did not make a backup, you can reinstall the game to get the default files.

Custom knife models may not work on all CS 1.6 online servers. Many servers enforce consistency checks and will replace your custom model with the server's default or kick you for file mismatch. You can only use custom models on servers that allow them or in local games.

CS 1.6 does not have a console command to change the knife model directly. The knife model is determined by the files in cstrike/models. To change it, replace the v_knife.mdl, p_knife.mdl, and w_knife.mdl files with your desired model. Some servers may use plugins to allow model selection, but that depends on the server.

Place the custom sound files in cstrike/sound, preserving the folder structure of the original sounds (e.g., weapons). The game will use them if the model references those sound files.