Since you will be making private channel, the mere "access/vanity code" to add it can be the secret shared only with the limited few friends. But, you can also do what you asked in three lines:
allowed_list = "123456789abc 123456789ab1 123456789ab2 ..."
serNo = createObject("roDeviceInfo"). GetDeviceUniqueId()
if inStr(1, allowed_list, serNo) > 0 then ' yes, device is on the approved list
Now, that's fine for a "toy channel" like this but let me disclaim that hacks like this should not be used for public channels: one, using S/N is discouraged (people sell/gift players, get new ones etc); two, hard-coding it like that is a pain to update the list - have to push new version.