"We've got a lot of confidence in Beaver," the coach said. "While he hasn't had a big history of playing 12, we're confident he can do the job.
"He's a real professional and has an incredible attention to detail. He'll be nervous - he was pretty nervous coming back in our environment. But he's also excited.
"He's a man for the big occasion. [The Stormers] have a very good midfield and they'll certainly challenge us, but one thing we know with Beaver is he's experienced and he'll really help Aaron [Cruden] with his voice."
Donald, who earned 83 caps in his first stint with the franchise, will link with Anton Lienert-Brown in midfield, adding an old head to a Chiefs team featuring a few young faces. The loose forward trio, for example, sees Sam Cane named alongside Taleni Seu and Tom Sanders, each set for their first taste of playoff rugby.
That would have been a different story had Liam Messam been declared eligible but, having played fewer than four matches this season, the Chiefs' all-time cap leader fell afoul of a rule Rennie described as "archaic".
"There's no doubt it needs to be looked at," he said. "You have to name 40 players at the start of the year and I think 12 of those 40 are actually unavailable for us now.
"We're pretty disappointed - as you can see from our bench it leaves us with a couple of sevens, which is not ideal. But we have a pretty good side on the field."
The other alterations to that side come at right wing and halfback, with Sam McNicol replacing Toni Pulu and Brad Weber earning the No 9 jersey. Tawera Kerr-Barlow had started the previous two games at halfback but, following a lengthy injury break, that was down to a desire to increase his playing volume.
"We're pretty fortunate that we have two outstanding nines," Rennie said. "Last week they split it 50 and 30 minutes and, while we don't really plan what time we're going to make changes, we're lucky we can bring on a different style of halfback to hopefully make an impact."
Rennie was predicting an "abrasive" game at Newlands, expecting his team to be challenged defensively and at the set piece. But after bowing out in the opening round of the playoffs to the Brumbies and the Highlanders in recent seasons, he felt his charges were this year better placed to reach the final four.
"We've stumbled at this stage in the last couple of years and we're certainly aware of that," Rennie said. "But we've talked about understanding the lift in intensity when you go into playoff footy, so we'll be well prepared."
Chiefs team to play the Stormers:
1. Kane Hames (7)
2. Nathan Harris (21)
3. Atu Moli (9)
4. Dominic Bird (9)
5. Brodie Retallick (69)
6. Taleni Seu (16)
7. Sam Cane (80) co-captain
8. Tom Sanders (13)
9. Brad Weber (40)
10. Aaron Cruden (71) co-captain
11. James Lowe (35)
12. Stephen Donald (90)
13. Anton Lienert-Brown (22)
14. Sam McNicol (10)
15. Damian McKenzie (31)
RESERVES:
16. Hika Elliot (102)
17. Siegfried Fisi'ihoi (9)
18. Mitchell Graham (24)
19. Tevita Koloamatangi (7)
20. Lachlan Boshier (6)
21. Tawera Kerr-Barlow (65)
22. Toni Pulu (11)
23. Shaun Stevenson (4)
