Penn admitted he was unlikely to get much sleep after Thursday’s 2-1 play-off eliminator defeat to Boston consigned Harriers to another year in non-league's second tier.
But the boss, who together with assistant Jimmy O’Connor this week signed a new three-year contract at Aggborough, promised to quickly turn his attention to the future as he works to improve his team.
Despite a memorable season which saw Harriers come within a whisker of beating West Ham in the FA Cup, Penn insists changes to the squad are inevitable. Those players out of contract will learn their fate next week, while the club are eager to move on a number of transfer targets.
Penn said: “There will be changes. It is a horrible thing to say but there are always ins and outs at every club up and down the country.
“That will be the hardest thing because this group have run through brick walls for me. But we have to be better to get out of this league. I have to identify what makes us better and move on from there.
“I’m pretty cold-hearted. I can dust myself down pretty quickly. We are back in pre-season training in five-and-a-half weeks so I have to turn this around pretty quickly. I will be on the phone tomorrow and come Monday I will be back at it.
“We have a nucleus of a squad. We will be looking to keep a few players, others won’t be with us and others will want to move on. That is the nature of the beast.
“We've identified players of interest. That is the way it has to be. I want us to be better next season.
“The hardest part for me now is to have those conversations next week because to a man everyone has done something this year. But it is going to be a rollercoaster summer.”
Harriers looked well set to challenge for automatic promotion when their FA Cup run ended in February but fixture congestion and a series of injuries to key players saw their challenge stall and they eventually finished fourth.
Influential skipper Sam Austin missed his only game of the campaign through injury against Boston and Penn admitted regret at not strengthening the squad when he had the chance.
“When we had the chance to recruit and we didn’t because we had a strong squad, that is probably why we missed out,” he said.
“You never know what is round the corner. One injury led to two and then to three and the strength of the squad wasn’t quite there. You need to be proactive in this game and that is something I have learned.
“Me and Jim are 36-years-old. We are young, energetic and naïve at times. But we want to be successful and we will do everything in our power to get that.
“We are disappointed now because we’ve had some success, liked the taste of it and want more. I’m greedy and that is why come Monday we are back at it again.”