Hi,
The tint swatches that you've created can be re-made using your new values. Once that is done, you can select the original swatches and delete them. Indesign will ask for a replacement swatch - just put your new swatch in.
Objects or text that don't have a dedicated tint swatch assigned to them can be found using the find/change panel, which will let you search for colours. Again, you can substitute your new swatches here.
Having said that, paragraph, character and object styles are invaluable in a situation like this. The change only needs to be made in one place if the document has been set up well using styles.
Regards,
Malcolm