@Emilio455 , @Dora676 , @William1254
Yes...Airbnb continues to make major software changes to the platform that affect 1000's of Hosts without notifying the Host community. This creates chaos for Hosts and negatively impacts guest. If I had to guess, the character limitation may have something to do with all the changes to the messaging system recently. They may have to do that in order to allow it to function properly. Be glad it's 4,000 characters...it was 3.000 until many Hosts recently complained.
That said....ok, you need to make a platform change that will affect many Hosts. Please let Hosts know so they can prepare and come up with other solutions proactively. I have advocated for a Host Bulletin Board secction on the main landing page, but alas, to no avail. Airbnb could use this to alert Hosts to major changes there and provide a feedback button for Hosts to use. At least Hosts will be prepared to deal with changes then:
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In the mean time, many Hosts create a document on Drobox or Google docs and put the link in the Airbnb Check-in message. This will help reduce the characters of the message. It may appear as the link is not functioning when creating the Scheduled Message, but it actually does work when the message is sent; I have done this for several Hosts and tested it. I like the Dropbox version as the document you create is "searchable" by keyword which is great for guests. Some Hosts also create their House Manual and post on Dropbox and do the same thing.