Comment by desdiv

>If not, would it be possible to build a device to flood them with fake/spoofed IMSIs?

Technical ability wise, yes.

Legally, no. The Mobile Telephones (Re-Programming) Act 2002 [0] makes spoofing IMSI, even that of your own, illegal in the UK.

[0] https://www.staffordshire.police.uk/info_advice/crime_preven...

Disclaimer: I am not a lawyer.