I-131 is the re-entry permit for PR.
It is good for 2 years, and you can renew for another 2 years.
But starting from the 3rd year, the officer will each time question you,
about whether you still have intention to permanently live in US and to
judge your tie with US. So you'll be risking your PR status.
I-131 doesn't protect your eligibility for naturalization.
You are still bound by 5-yr rule, that during the past 5-yr period you've
been living in US for at least 30 months in total, and any trip outside US
cannot be more than 6 months. If you've been staying for more than 6 month,
even just by 1 day, your total length of stay will be reset to 0, and the
new 5 year period is counting. Or even if you meet all trips less than 6
months outside of US, but you cannot meet the 30 months criteria, you cannot
apply for citizenship, and can only return and stay in US for enough time.
The only exception if you want to stay longer than 6 months, is to apply for
N-470 form, which will count your time outside US as part of the 30 months
required. But you have to prove you are working for US business.
