I have an original raster file called SAM. This has a resolution of 0.0025 pixels, it was obtained using 100m resolution satellite. I have another raster called Global fire. This has a pixel resolution of 463.3m using a custom CRS. I converted the Global Fire CRS to be the same as the SAM file to see what 463.3m in pixel resolution was equivalent in georeferenced units like the SAM file. This was the value 0.00205... I then did a reprojection of the original raster file SAM to convert its resolution to have a pixel size of 0.00205 to match the Global Fire pixel size. My question is that is this methodology fine. Have I essentially now converted the SAM to now have a resolution of 463.3m resolution this way. I did this because I couldn't get that custom CRS to go on to the SAM file. I look at the actual resolution on the screen and it doesn't look too different so I figured I may have done something wrong?
Seems to be some confusion here. If you have a satellite image at 100 m resolution, then that's its resolution. Each pixel is 100 m. (saying "resolution of 0.0025 pixels" does not make sense). If you want to know the equivalent size of a pixel from some other coordinate system, just convert the units. (No need to reproject).
When you say: "I converted the Global Fire CRS to be the same as the SAM file" I hope you did NOT set the projection. That's the most "popular" error with CRS conversions.
If you need to do some coordinate transform you have to know exactly what the current CRS are for both rasters. With more details regarding both rasters someone will surely be able to offer more help.