Is it possible to have Apple update RAM in current Mac mini (Late 2014)
Short answer:  No.

Apple is not going to retrofit memory into any Mac (Mac mini, MacBook, etc.) if you want to upgrade.  They don't even make simple repairs to their logic boards - they will just replace them.   

If you require more memory, you will need to 


replace the logic board
purchase an entirely new unit


While I typically would purchase a machine (Apple, Dell, Lenovo, etc.) with the highest CPU and lowest memory and drive specs, this has now become impossible since RAM is now commonly soldered on and in the case of Apple, their SSDs are proprietary.

Buy the machine with the specs you think you will need in the future, not for what you need now.