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Worth discussing with the engineer how changes will be dealt with. E.g. architect specifies opening size, engineer says it can't be done without [thing]. So now you have to pay architect to do more work, then pay engineer again to redo their bit.
Architect and engineer involved will be able to tell you more but my point is that the engineer fee is not going to get lower, and could quite reasonably go up, perhaps up to an order of magnitude more if weird or unexpected stuff comes up.
It's just for the specs of the beam we need, no architectural drawings