The health guidelines or protocol to be followed when allowing in tourists with relaxed quarantine procedures has been reported on in the media. A copy of what I believe are the guidelines is linked here:
Health Guidelines for Tourism Pilot Project

These guidelines appear to be issued by the Minister of Tourism and were sent to the Chairperson of the SLTDA on 27 December 2020.

Somewhat surprisingly, the guidelines says that incoming tourists will be tested on arrival, and again at 5 and 10 days after arrival. It makes no mention of pre-flight tests, although my recall is that this was mentioned previously, and this is also reported by this news report in EconomyNext.

Another curious aspect is that these guidelines are issued by the Minister of Tourism and not by any health official. This confirms my sense that the health authorities are increasingly being sidelined in the setting of the COVID-19 response. To some extent this is understandable since the health authorities failed to prevent the second outbreak, largely due to their failure to invest in testing. However, the consequences of this trend are likely to be severe and bad for the country, our public health and our economy.

If anyone has a better or more comprehensive version of the protocols, please let me know, so I can update this.