Severus rarely felt this relaxed with another person in the room. Certainly, he was more comfortable eating here than in the Dining Hall - where having all four Marauders present brought back a lot of very bad memories - but he'd never been this relaxed on the occasions he'd eaten dinner here with Albus and/or Minerva. He knew why, of course. Albus was... Albus and Minerva didn't know the extent of what he was doing. Regulus, on the other hand, was a friend and someone he trusted with those parts of himself that others usually rejected.
He looked around the room at Regulus' comment and grimaced a little. "I can make a few changes but the school and room resist too much in the way of it. The Headmaster's office is apparently meant to be some kind of monolith. The Headmaster may change but the room stays eternal or something along those lines."
A few of the Headmasters in the portraits, the ones who hadn't already nodded off - or wandered off - murmured and nodded in agreement. Severus ignored them with the ease of long practice.
He gestured towards a closed door nearby. "Thankfully, the castle doesn't insist on the same for the personal quarters and it allows for a workroom to be opened up as well."