I would avoid doing this at all costs as you may wind up with an exploding lamp or a ballast fire!
Like funkybulb said you are new at this and may wind up hurting yourself!
Trust me, I found out the hard way!
I ran a 50 watt MH lamp on the wrong ballast and it exploded and I wound up with glass in my face and a lifetime scar!
Learn a lot more BEFORE experimenting!

Was the MH lamp on a ballast with slightly higher voltage and current characteristics?

I also see some citations stating that the Philips SON-H 68w HPS retrofit lamp for European 80w MV lamps have very similar operating characteristics compared to US 100w H38 MV lamps. From what I see with the Philips SON-H 68w HPS retrofit lamp according to the engineering leaflet, I see that the lamp operates between 92v-122v 0.84a while according to the US Sylvania engineering bulletin for MV lamps, it says that 100w H38 MV lamps operate at 130v 0.85a while Colin Grimes cites both of these lamps operating at 130v 0.8a. In addition, I see that according to the Philips 80w HPL-N lamp engineering bulletin, I see that the lamp operates at 0.8a and has an arc voltage between 105v-125v. According to this data, it seems to show that The Philips SON-H 68w lamp, the Philips HPL-N 80w lamp, AND the US 100w H38 MV lamp truly have very similar operating voltages and currents that only differ differ by small margins. That is proof that European 80w MV lamps are safe to operate on US 100w H38 HX mercury ballasts PERIOD.

Here is the Philips SON-H 68w engineering leaflet (look at the first and second pages):

https://www.lighting.philips.com/api/assets/v1/file/content/fp928494909891-pss-global/ADAM-20151211073741247%40en_AA.pdf

Here is the US Sylvania Engineering bulletin for MV lamps (look at page 7):

https://media.distributordatasolutions.com/Sylvania/v1/files/File_Technical_Document_-_High_Intensity_Discharge_MERCURY_Lamps_69408.pdf

Here is the Philips HPL-N 80w MV lamp engineering bulletin (look at the first and second pages):

https://www.lighting.philips.com/api/assets/v1/file/content/fp928051007391-pss-global/928051007391_EU.en_AA.PROF.FP.pdf

For these reasons mentioned above, i see no reason why a European 80w MV lamp will quickly burn out, explode and catch things on fire, and cause ANY damage to a US 100w H38 HX MV ballast. As other members have said, they have known about 60w SLI/H lamps being able to operate safely and last their rated lives on European 80w MV ballasts and European 80w fluorescent ballasts despite the fact that European 80w MV lamps run at 105-125v and 0.8a while the 60w SLI/H lamps operate at 80v 0.83a. In addition, Globe collector told me that on HX ballasts, the ballast does not have a set output voltage and that he tells me that the lamp current from HX ballasts will dictate the lamp’s operating voltage.

Ok, let's not get into any arguments here. We all have our own opinions, which we are entitled to. What none of us is entitled to do is to ram our opinions down other people's throats. Tone it down, please.

No you are wrong. He is right. Look:

http://www.lamptech.co.uk/Spec%20Sheets/D%20MB%20Sylvania%20H100-C.htm

You are wrong. 100W MV are 0.95A lamps (the H38), so the 80W (0.8A) would be overloaded.
Arc voltages are around 105..110V for both 80 and 100W lamps.
130V is only for tye higher power, like 250W or so.

Yeah H38 lamps are listed as 0.85A @ 130v in the Sylvania literature.

The JIS 100w lamps are 1.00A @ 115v so I don't know where 0.95A comes from...

I have seen people saying that the Japanese 100w MV lamps will work fine on US 100w H38 MV ballasts too.