Whenever I am reading annotated games books, there are various alternative positions too given by the author . in that case it becomes too complicated to practice on real board else it will spoil the actual game . In that case do you know of any website which also has variations as mentioned by the author that can be worked out while simultaneously being able to return to the actual game eg after a move variations are given in the bracket to be worked out

I don’t know such a site but i can share that ICC has library accounts for the following books.  These are just the moves themselves no annotations but for example when viewing my system you can bring the game up on an examine board to play through on icc.

Accounts:

AkibaRubinstein   100 games from Hans Kmoch’s book ‘Rubinstein’s Chess Masterpieces: 100 Selected Games’ library by autobot
ArtPosChess     ‘The Art of Positional Play’ by Samuel Reshevsky. library by autobot
Greatest100     Games from the book ‘The World’s Greatest Chess Games’
Greatest100b     by GM Nunn, GM Emms and Graham Burgess
HAL9000       Game from movie ‘2001: A Space Odyssey’
MyGreatPred-1a   ‘My Great Predecessors Part 1’ by Garry Kasparov.
MyGreatPred-1b
MyGreatPred-2a   ‘My Great Predecessors Part 2’ by Garry Kasparov.
MyGreatPred-2b
MyGreatPred-3
MyGreatPred-4a MyGreatPred-4b   great pred libraries by autobot
mysystem       Games from the book ‘My System’ by Aaron Nimzovich (capa1)
My60MemGames     Games from the book “My 60 Memorable Games by R. Fischer (Lyon)

To open these libraries on BlitzIn type for example /liblist mysystem then right click on game you want for a popup menu to select examine. 

On Dasher type /finger mysystem     then it opens the profile view and click games tab at top and again right click on game for examine option.

On icc for windows and mac go to the lookup user icon on the toolbar ( 4th from right) and type for user     mysystem and you will have the profile view with the library.

Mike