Assembly transfer to another subsidiary. This item is treated differently in those two subsidiaries. 1st subsidiary manufacture those assemblies and asset account on the item is XXXXX. The second subsidiary buys those assemblies from the 1st subsidiary and for them its just item for resale ant not a product (assembly in Netsuite terminology) anymore so the asset account should be different lets say YYYYY. How to solve such situation as the asset account on the item record is only one?

I am not a functional consultant but I think you can resolve this by creating 2 items. Once you received the required item from subsidiary 1, do an inventory adjustment (via customization). May be someone else can confirm this.