Inquiry about how PO charge account is defaulted

One item is set as non-stockable and non-transactionable but it has costing flag enabled and assets flag enabled at item master. As I know, as long as the costing flag is enabled, the PO charge account at PO distribution window is defaulted with material account set at ship-to Org. However, in our case, the destination type at PO is expense, and PO charge account is defaulted with expense account at item master level. The details are attached.

May I know whether the PO charge account should be defaulted with expense account or material account based on the above item setup? Is it true that when the destination type is expense, the charge account will be expense account? After the PO is created, can we override the defaulted PO charge account with any desired account? If we override the account with the desired account, will this new overriden charge account be used in invoice accounting?