I was looking through my 9th grade civics textbook on the working of the legislature in India. It showed that there was a Office Memorandum that reserved 27% of seats for socially and educationally backward classes. Why didn’t the government amend the constitution rather than creating an office memorandum? Do different laws have different representations (constitution, memorandums, etc.)?
A memorandum is a short piece of writing designed for communication within an organization. In your context it is a mode of communication between different branches of government. It is also the official proof for a particular message being transferred. In the 27% reservation example it didn't require any amendment as the constitution had already given powers to the government to implement reservations.
Art 15(5): Empowers Legislatures to provide for reservation for any socially and educationally backward class including SCs and STs in educational institutes including private unaided institute. (Though same has not been provided in private unaided institutes) [Inserted by 93rd amendment, 2005]
Office memorandum is not any representation of a law.
Laws are of many types. A few major ones are :
Constitutional law, Like fundamental right etc. (What was already present in the constitution)
Statutory law, These are the laws passed by Legislature, using the process that the constitution describes (pass the LS, pass the RS, presidential approval)
Common law, which is law made by judges.
Administrative law, which is made by executive agencies. The 27% reservation law comes under this.