Is it necessary to customize letters of recommendation with recipient names? I am concerned to the fact that how a professor whom I am asking to write an LOR, will change the name of the person every time before sending? I am applying to like 100 different persons for the position of postdoc. Does it really matter that it should be addressed appropriately (name basis)?

I am working in the interdisciplinary field of materials chemistry, nanotechnology, environmental remediation, physical and theoretical chemistry.
I can hardly see the need of addressing the reader in a letter of recommendation, but if your professor wants to do it, they can use a process called mail merge.

Common word processors have mail merge functionalities (e.g. MS Word).