Out with the old, in with the new. Gone are the days of going to a Police Station and simply 'switching model' into a police officer. Instead, LSPDFR 0.4 is based around actual Characters. They have names, they have stats - they are their own person.
To play LSPDFR 0.4, you'll need to have at least one character. By default, LSPDFR 0.4 comes with a number of 'preset characters' which can be selected from. These roughly represent the options available in LSPDFR 0.3 and are intended for those who wish to jump straight into the action without creating your own Custom Character.
Custom Characters are those which can be created through the Character Creator in LSPDFR 0.4. We use the same system as that found in GTA Online, allowing a great detail of customization ranging from hair color to nose shape. They uniquely represent each player in the game world without having to worry about running into your doppelgänger.
Note that there's a limited number of police-related clothing and accessories available for these characters by default in Grand Theft Auto V. This can be vastly expanded by installing other modifications, like EUP, which adds hundreds of different clothing items and accessories for a large number of police agencies.
@Sam has also created a simple modification which enhances the LSPD outfits: https://www.lcpdfr.com/files/file/22116-lspd-character-outfits/
A Preset Character, on the other hand, is based on an existing NPC model. This gives them a great range of available clothing and components, but ultimately limits their individual look. Players that have played LSPDFR 0.3 will recognize most of these models. While a preset character is still essentially a normal character, that can be used to LSPDFR and also synced to your account, there are certain limitations. Most notably the lack of a proper off-duty experience since a NPC character does not have an off-duty outfit. For the full LSPDFR experience we hence recommend using a Custom Character.