yes of course , first you have the native who is universal for any gta framework , you just have to replace the native calling who can be different depending the framework. for the native : http://runtime.fivem.net/doc/reference.html
but it depend what language are you using , if it’s c# you have everything listed in the dll directly.
if you code with lua , you have most of function in your appdata/local/fivem/scripting/lua/
it’s not that hard , it’s just a question of analyse and logic , if the script you want to convert use Vehicle object who is in the ScriptHook.ddl , then you will have to change the code for using the one from CitizenFx.dll , but the object will certainly have different param name ect so you have to change and adapt all the calling. i don’t know if what i’m saying it’s enough clear.