An image’s profile and its pixel values have related but different jobs. Replacing the profile is not automatically the same operation as converting the image to another colour space. Decide which problem you are trying to solve before choosing the option that makes the preview look most pleasing.

Keep the original file untouched and open a clearly named working copy in ColorSync Utility. Record the image’s known source profile and the intended destination requirement. If the source interpretation is unknown, do not turn a guess into a claim about the image’s original colour space.

Choose the operation by what it changes

Apple documents Assign Profile as changing the image’s profile without modifying its stored image pixels. Match to Profile transforms the pixels for the new colour model and profile, then assigns that new profile. Apply Profile also transforms pixels but assigns the original profile afterward; it is a different operation.

After File, Open, the lower-left menus select the operation and profile, while the lower-right menu selects intent. Apple states that Apply saves the change to the file. Review the working filename and operation before pressing it; previewing alternatives is not a reason to overwrite the only source.

Consider two different requirements. If a known profile tag was omitted from a file, the question is how its existing values should be interpreted. If correctly interpreted source material must be delivered in another specified profile, the question is how to transform it for that destination. Those requirements should not share one unexplained instruction to “change the profile”.

Retain the reason for the conversion

For a supervised comparison, prepare separate copies and label each with the chosen operation. Keep the same source and viewing conditions so the operation is the variable under investigation. Do not silently chain several conversions and then compare only the last file with a remembered appearance.

Inspect important colours and fine gradients, but keep visual preference separate from evidence about the correct source interpretation. A more saturated preview cannot establish that an undocumented profile was the one originally intended. When exact colour is contractual, use the project’s agreed colour-management process.

Hand over the accepted file with its source and destination profile identities, operation and intent recorded. Retain the original until the delivery is accepted. This makes a later correction traceable to a deliberate transformation or tag assignment instead of an undocumented attempt to make one display look better.

References: Apple: image profile operations.