The Empadron does not affect your tax status. It is the register of people who live in a municipality and is a legal requirement. That said, some municipalities allow or even encourage everyone who owns a property to register even if they spend only holidays here, as the town hall receive allowances from central government based on the number of citizens registered on the Empadron.
However (and I have confirmed this with the Spanish tax office, although I know people will disagree) once one has registered on the EU Citizens Register with the National Police (and got the certificate on green paper) they are tax resident in Spain. An example is that my friend’s bank froze her non-resident’s account when they were internally informed she had registered.
The183 day rule, says if one is physically present in Spain for a total of that period in a year, they are automatically tax resident and liable to pay tax on their worldwide assets (excluding any which are included in Double Taxation Agreements). That means; if does one register, say because they are not permanently here for 90 days, i.e. they leave after 85 days for a day or two, they automatically become tax liable.