Sed - Replace lines with pattern matching with string

I've got this file i'ld like to work on :

{'ID1': {'Zero': u'value', 'One': 'value', 'Two': 'value', 'Three': 'value', 'Four': 'value'}, 'ID2': {'Zero': u'alue', 'One': 'value', 'Two': 'value', 'Three': 'value', 'Four': 'value'})

I've got this sed liner to get single properties :

sed -n '/ID1.*{/,/}/p' file

That will give me this :

{'ID1': {'Zero': u'value', 'One': 'value', 'Two': 'value', 'Three': 'value', 'Four': 'value'}

What i'ld like to do is to replace that output with a STRING

Can't figure it out how.

Any help will be appreciated, thanks!