It is a WIM file now.
If you have your 9.0 install files (extracted), then you can get the default Boot.wim by searching inside it.
Unfortunately I haven't investigated which mods if any are made during install.
We do make some mods. The SAFEST way (albeit time-consuming) I can think of to get your WinPE image back is to spin up a VM, install a core server to it, copy your certs into the new core, and activate your WinPE license from the WAIK.
I'm thinking there may be a way to fool Management Suite into thinking the WAIK hasn't been verified yet, but I don't know if it'll throw errors for the files already being present. I've never heard of having a corrupt WinPE before...
I know it must have changed to core server name because when I copy a new .wim file to replace the corrupt one and then try to run a capture image script, it comes back saying it can't find %coreserver%. Any idea where that gets updated or how to update the .wim file?
In the previous article that is only for 8.7 and 8.8's LDVPE1.img there is a mention of the ALL.REG file.
However that article needs to be updated for LDMS 9. Use this article to modify the image and update your ALL.REG.