this is an interesting question and before reading on, please understand that due to complex nature of process's interlinking plus production situation, each step (cancel/delete/add) possibly can have multiple  scenario possibilities..
to keep it simple, lets start with simplest.

Cancellation ( being the easiest one )

Scenario 1: Full / Completely Cancel

if you hit cancel button, this surely does few things.

• make sale order status to cancel

• another button appears to set its status back to quotation (kind of reset)
  

• also linked delivery (pick pack ship) -> inventory actions to cancelled as well.

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• more importantly, what i want user(reader) to understand is that it hasn't tweak/change manufacturing(linked orders) directly, but it has logged a msg to MRP team that things have changed and need attention.

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Scenario 2: Partial Cancelling some items.

after confirmation, if you edit sales order, you will see those buttons -> SOL(sale order line) right

if you delete an item(article), odoo will give you wanrning msg to please go and edit related (pick pack ship) receipts and make sure, corrects articles (amounts) etc will be sent to client.

TBC ( will write more soon..)

actually adding items is similar, odoo will generate newly added items MO as well (that is awesomeness)

increasing/decreasing quantity is also similar, except the fact, you have to update MRP dept as well (i still haven't confirmed log msg etc)