F1 World, changing engineer supplier

For clarity I am refering to the Custom cars in F1 world. 

I'm confused by your question. By "enigineer supplier" do you mean "engine supplier"? Also, by "custom cars in F1 World" do you mean the World Car? If so, you have flexibility to change and dismantle the type of engine (the term used in F1 World is power unit) but you have to win these parts from races or build them in the Engineer Parts feature. If I misunderstood your question, do you have a link or screenshot where this feature was promised?

You are correct , my silly phone with it's predictive text lol. Yes I meant Engine Supplier in F1 world, whilst using F1 custom car. 

Also, when you say you have to win these parts from races or build them in engineer parts feature, does this mean that for example if I win a 'Legendary' power unit & and replace the existing 'Rare' power unit, the engine will sound different ? I.e Renault to Ferrari , Mercedes to Honda and vice versa ? 

I appreciate your prompt & brilliant response , wish you a great rest of the week & Happy racing buddy :)