The FT8*7 series has three power levels that can be selected in each set of bands. The 6m, 2m and 70cm bands each have their own settings.
For each power level, there are two settings, one being the output power and the other more important one being the RF driver gain.
If the 2 watt level has been configured correctly, the radio won’t be able to output a 50w spike because the drive level will have been set appropriately, so that the radio will only just make the power level set as the maximum ie 2w.
If the user performs a super master reset, all the control levels are set to max. In that situation, all power levels are the same. If the power is cut back using the ALC setting, leaving the gain set to maximum, the 857 is then capable of a 50w spike followed by the gain being reduced by ALC to the preset output limit. IMO these power controls are more suitable for FM modes than SSB. Using the radio to drive a transverter is outside its designed application, so some extra research is advisable.
The bottom line is that if the radio has been configured using the factory procedure, and you set it to a lower power level, eg 0.5w or 1w in the case of the 817, you should not get any power spikes higher than the nominated level.