As MEI calculations are based on annual values for Risk, Residual Risk and Maintenance task costs, one-time changes that have up-front cost instead of recurring costs do not fit in the calculation.
So, to deal with this one might need a 'trick', which is by definition, a suboptimal solution.
It is suggested that if 'one time cost' are made related to a maintenance strategy, that you might expect that if the failure occurs once again - after all - that you may need to reconsider the 'one time cost' effort - for an adjustment.
In such a case the one time cost could be taken on board as 'One-time-cost / ETBC' in USD/yr.
In IMS you can put it in a task under Miscellaneous Cost - by 'One-time-cost / ETBC' (USD/yr) x task interval (yr):
So: if you have one time cost of 5 kUSD, and an ETBC of 10 yr, you have 0.5 kUSD/yr cost.
If the task is done every 2 years, you can put in Miscellaneous Cost of 1 kUSD - on the task.
This approach gives a 'return of investment' of the one-time cost of 10yrs, where, alternatively, you may opt for – for instance - a return of investment of 4 yrs.