What are the CVAR differences between ETPro and Legacy mod? Can I use my ETPro config on Legacy mod? - ET-Legacy-Competitive/faq GitHub Wiki

In general, you can use your config from ETPro on Legacy mod, however it is NOT recommended. Preferably, you should create your Legacy-specific config from scratch.

What are the main CVAR differences between ETPro and Legacy mod? Some CVARs from ETPro won't transfer directly to Legacy (namely - all ETPro-specific b_ CVARs), but they can have their cg_ CVAR equivalent. In addition, some CVARs were deleted, changed or added.

The most important CVAR differences between the 2 mods:

all bobbing CVARs've been bundled into one "cg_bobbing" CVAR. Set to 0 to disable bobbing altogether;
"cg_tracers" instead of "b_tracers";
"cg_muzzleFlash" instead of "b_muzzleflash";
"cg_fireteamlatchedclass" instead of "b_fireteamlatchedclass";
"cl_activatelean" instead of "b_noactivatelean";
"cg_drawranks instead of "b_drawranks";
"cg_hitsounds" instead of "b_hitsounds";
"cg_altHud" instead of "b_althud";
"cg_altHudFlags" instead of "b_althudflags".

Other important CVAR changes and other issues you should be aware of:

"dropobj" command has been added - you can now drop the objective with a command instead of selfkilling;
setting "cg_drawGun" to "2" will disable the view of SMG and pistol, but'll keep the view of everything else - you don't need to tinker around your config to achieve that anymore;
you can now set "cl_maxpackets" up to 125;
you can now set "rate" up to 45000;
you can now set "com_maxfps" up to 250;
you should NOT use OpenAl sound system - use SDL instead: s_initsound “1".
setting "r_depthbits" to 32 can cause FPS drops;
"cg_wolfpartciles" CVAR's been removed - you can't disable explosions.
it's recommended to pay extra attention to your renderer (r_) CVARs if you're trying to use your ETPro config on Legacy mod;
simple items' design was reworked - make sure to check it out.

Credits: @ryzyk-krzysiek