Are you sure you looked at the correct part #.
I don't know the last 7 of your vin for 100% accuracy, but they should be #11 62 7 662 083(or 11 62 1 464 061 crosses to the other) and unless you have super atrocious shipping to Ireland they are less then $4 U.S. each. (2.10 inc vat from Motobins)
https://motobins.co.uk/bmw-parts.php?model=K%20Series&bikeref=K100Do you absolutely change them? It's up to you. If you were refitting the same exhaust that seated them I would say probably not, that they would seal again. Since you are fitting a different set of headers, I'd bet that they wouldn't seal correctly and I would recommend changing them.
You can always just put the exhaust on and try it. It may work, it may not, then you will know--
Re the bolts, replacing them is totally up to you. Not really necessary unless you break one.