I tested it and I've found two issues, one minor and one existing but exacerbated. But first I want to state that Concrete Piercing Round functions exactly the same regardless of what you have loaded.
1. The ISU no longer aims the gun, instead it points forward and shells just curve-ball their way to where it was aiming. Looks funny, but it's only a cosmetic issue.
2. Concrete Piercing round can be fired instantly after an HE or AP round, this is exacerbated with AP allowing you to hit a tank, then follow-up with another hit immediately after.
ISU has always been able to fire concrete round right after a normal round - it has been a bug for a long time unfortunately.
As I was saying in the shoutbox though - if this ISU is the one Relic had us testing on the balance servers these changes for the ISU and the JT are hugely welcomed. The ISU should now rarely, if ever, 1 shot a full health squad. I'm sure it'll happen every once in a while to some bad RNG or being hella clumped up but it certainly isn't going to be wiping 10+ squads per game as it does now.