How can I modify 100 instances at once instead of changing one instance at a tim

I assuming you are talking about process instance. Use IFM Manager:
forum.appian.com/.../summary

Are you asking about changing something in 100 running process instances or modifying 100 variables in a single process?

Hope this helps.

forum.appian.com/.../summary

@ankitab Ideally bulk in-flight modifications (For instance, shared components at https://forum.appian.com/suite/tempo/records/type/components/item/i8BCLGOdlMUpdGVqT-RV7oRg74uEGJO5CMZACzz_5W0L-UUHaRsMA-2Or_cSO-8rg/view/summary or https://forum.appian.com/suite/tempo/records/type/components/item/i8BCLGOdlMUpdGVqT-RV7oRg74uEGJO5yMZhxXUTN1sqvlBkRVMp8r3HMsZI2HLIg/view/summary or https://forum.appian.com/suite/tempo/records/type/components/item/i4BCLGOdlMUpdGVqT-RV7oRg74uEGJO7Cf7SfSAexBTrc2mR34kKManhy4Qdg8C/view/summary or https://forum.appian.com/suite/tempo/records/type/components/item/i4BCLGOdlMUpdGVqT-RV7oRg74uEGJO7ST7vajpgHr5N88A8C7XkID6LIPzexYr/view/summary) should aid you in doing so to the best of my knowledge. I would like to suggest to go through them if you haven't explored them till date. Further you could expect a answer quite apt to your question if you could elaborate the use-case and also the community could come up with best possible approaches.
Also I would like suggest you to go through https://forum.appian.com/suite/help/7.10/Process_Upgrade.html and https://forum.appian.com/suite/help/7.10/Process_Upgrade_Planning.html to gain a bird's-eye view on these modifications and their impacts. The documentation also has suggestion for us about the component we can use for doing so.
Not quite sure, but I heard that https://forum.appian.com/suite/tempo/records/type/components/item/i8BCLGOdlMUpdGVqT-RV7oRg74uEGJO5icQMwg8v5zXc-t_9wkguEBhUYdRv_DvUQ/view/summary is a good component to start getting on with this part it seems.

@peterf: i am asking for both

Thanks guys..This helps alot