To change the default processing settings in Lightroom Classic, use the following steps:
1) Select a raw file taken with your camera and remove any settings by clicking the Reset button in the lower right of the Develop Module.
2) In the Basic panel, select the desired profile.
Note: changes are not limited to profiles. You could, for example, also enable the Lens Corrections options or customize the amount of Noise Reduction applied in the Details panel – just remember that your new default settings will be applied to ALL future images imported from this camera.
3) Choose Develop > Set Default Settings > Update to Current Settings. Note: Although the dialog says that the changes are not undoable, it only means that the shortcut Command + Z (Mac) | Control + Z (Win) won’t undo the settings – at any time you can return to the dialog and choose Restore Adobe Default Settings if needed.
Once the defaults are changed, any images taken with that camera model will automatically have the profile applied when the are imported into Lightroom (any images that are already in the catalog remain as they were).
Option (Mac) | Alt (Win) toggles the Reset button to Set Default (in the Develop module) to quickly access the dialog.
If you are using multiple camera models, you will need to customize the default settings for each model (by following the above steps for each camera model).
It is also possible to save different setting for each camera based on serial number and ISO settings (Preferences > Presets). This can be useful when using custom camera profiles for example.
If you choose to enable Lens Corrections, if you change lenses, Lightroom will automatically look for and apply the appropriate lens correction profile based on the EXIF data in the photo. If you import 1000 images but will only end up using 10 of them, applying lens corrections to every file that you import will increase the amount of time it takes to render previews (how much time depends on your system, file size etc.). If you notice a significant decrease in performance, you might prefer to create a preset to apply lens corrections, and apply it to only your best images.