The former defender has been put in temporary charge for the upcoming two friendlies - the other being against Switzerland next week - and he has opted to stamp his mark on the squad.
On the back of his outstanding form for Blackburn Rovers in the Championship, Szmodics is selected in what appears to be a front three alongside Chiedozie Ogbene and Evan Ferguson.
Liverpool goalkeeper Kelleher also gets the nod over Gavin Bazunu between the sticks, reward for his consistent performances for the Premier League giants.
Nathan Collins, Andrew Omobamidele and Dara O'Shea will seemingly form a back three, with Seamus Coleman and Robbie Brady being selected as wing-backs.
In total, there are seven changes from Republic of Ireland's game competitive game against the Netherlands, the Boys in Green losing 1-0 in their final Euro 2024 qualifier in November.
Meanwhile, Belgium boss Domenico Tedesco has also named what is an experimental side, the likes of Jan Vertonghen and Romelu Lukaku only being selected among the replacements.
Genoa defender Koni De Winter is handed his debut, while left-sided player Olivier Deman - who represents Werder Bremen - will be earning just his third cap.
In midfield, Aster Vranckx and Arthur Vermeeren will be winning just their fifth and third caps respectively, with Lois Openda leading the line.
With Kevin De Bruyne, Lukaku, Vertonghen and Thibaut Courtois all not involved, midfielder Youri Tielemans has been given the captain's armband.
Republic of Ireland: Kelleher; Collins, Omobamidele, O'Shea; Coleman, Cullen, Smallbone, Brady; Szmodics, Ogbene; Ferguson
Subs: Bazunu, Travers, Manning, Doherty, Idah, O'Dowda, Sykes, Johnston, Knight, Obafemi, Ebosele, O'Brien, Azaz
Belgium: Sels; Castagne, Faes, De Winter, Deman, Tielemans, Vermeeren, Vranckx, Bakayoko, Openda, Trossard
Subs: Casteels, Kaminski, Bodart, Batshuayi, Debast, Doku, Lukaku, Lukebakio, Mangala, Meunier, Onana, Theate, Vertonghen