First define character styles that do nothing but change the font style to italic, bold, and bold italc (or others if you need them). Use Find/Change to apply the character styles to the text where they need to be assigned (and this can be time consuming) or consider using a script like PerfectPrepText: A smart way to style local ... - InDesign Secrets
Then don't use Find/Change to change the font. Instead edit the style definition for the style applied to the text.
Thanks Peter for the fast reply.
I am trying a couple of options as you suggested but it seems i am doing something wrong.
I do not have all italics as character style since i have imported or placed with basic paragraph which i guess it is easier for very long documents. Maybe i should have imported as an italic character style...but the book is almost finished now. I should start again.
I will try the script you suggested if i can make it work now.
All text has a paragraph style which applies the basic formatting for the entire paragraph. ANY text that deviates from the general formatting of the paragraph should have a character style applied in some way, either directly or as a nested or GREP style, that overrides the paragraph formatting and gives what you want. Paragraph styles that do not change the font family are far more useful, such as a style that simply changes the text to italic, since they continue to work when you change the font family in the basic text format section of the paragraph style.
Character styles are used ONLY to change part of the text in a paragraph. If the whole paragraph has the same formatting, it should have a paragraph style defined for that format.
Thanks for the good info P.
I will try to follow that structure to solve the text issue.