Large individual differences have been documented among users in their multimodal integration patterns, which suggest that new user-adaptive approaches to multimodal fusion may be opportune. Before pursuing such an approach, this study explores whether people can be successfully encouraged to switch their multimodal integration pattern to one that is easier to process through the use of explicit instructions. Longitudinal data were collected from young and elderly adults as they used speech and pen input with a simulated map system. Results revealed that only 37% of users switched their integration pattern and maintained it, whereas another 19% never switched their natural pattern and 31% switched but then reverted during a follow-up session. In addition, significant destabilization of elderly users' integration pattern was one "cost" of attempting to instruct a change in pattern. This research underscores the need for user-centered design in future multimodal system development, especially for vulnerable users such as the elderly.