You can renew your IR without having to rewrite the exams again provided that your IR has not lapsed by seven years. It used to be five years but that has changed relatively recently.
How do I know this? Because that is exactly what I have just done. My IR would have lapsed by seven years this month. I renewed it in August. My Class 1 medical was tricky and I had to do more or less the whole lot at the Beehive. But then you actually only need a Class 2 if all that you want is PP privileges with an IR.
In my case I shall probably never fly commercially again but I renewed my ATPL for one of those indefinable reasons that afflict mankind from time to time and are probably born of lust or over inflated ego. At least I could fly to the south of France IFR in a Baron............or someone might be sufficiently moved by my story of heroism as to give me a job in flight ops telling pilots how we did things in the old days!
PM by all means if I can help with further information on vainglorious acts of bravado and misplaced heroism.