I sometimes see in the RID the following phrase: "โดยปริยายหมายถึงอาการที่คล้ายคลึงเช่นนั้น" at the end of a definition. Does this mean that the term or phrase also has metaphorical meanings derived from the basic literal meaning?

How would this be stated in English?

Thanks.

Indirectly it refers to situations similar to this. It is always followed by an example in my experience to clarify how it is used. ie. ประคอง for instance is the physical act of supporting someone your self etc. but can be used in an indirect way ie. to support the government in a situation.

In the definition of โดยปรียาย where is says indirectly and complete departure from the direct meaning given, and uses the verb to parachute from a plane and to parachute from school or work. โดดร่ม = หนีโรงเรียน

You've understood correctly. It means by extension, or figuratively. A new meaning abstracted from the literal meaning.

If you're interested into the origins of the word, it's from the Pali pariyāya. Its Sanskrit reflex is paryāya (bottom of the center column in that image).