I am not sure about via the CLI or Web UI but you can edit the viewstates.conf if needed, however the mapping between the saved search and the vsid can be a bit cryptic at times the first time you see it.
Lets assume you have a savedsearch.conf entry that looks like this:
[Media - Report - RTP Errors - Last 4 hours] dispatch.earliest_time = -4h@h dispatch.latest_time = now displayview = report_builder_display request.ui_dispatch_view = report_builder_display search = rtpstat | extract rtpstat | where rtpErrRXTooMuchProcessed > 0 OR rtpErrNoData > 0 OR rtpErrRXUnterminatedDTMFs > 0 OR rtpErrRXSpamPackets >0 OR rtpErrRXProatvDroppedPkts > 0 OR rtpErrTXSendErrors > 0 | timechart sum(rtpErrRXSpamPackets) sum(rtpErrRXTooMuchProcessed) sum(rtpErrRXUnterminatedDTMFs) sum(rtpErrRXVoicePktDroppedDurDTMF) sum(rtpErrTXSendErrors) vsid = *:gd1t63rz
What you can do is look up that vsid (gd1t63rz) in viewstates.conf to find the formatter for that view:
[*:gd1t63rz] ChartTitleFormatter_0_6_0.default = RTP Error Counts ChartTypeFormatter_0_4_0.default = line Count_0_3_0.default = 50 DataOverlay_0_5_0.dataOverlayMode = none DataOverlay_0_5_0.default = heatmap FlashChart_0_4_1.height = 504px LegendFormatter_0_10_0.default = right LineMarkerFormatter_0_7_0.default = false NullValueFormatter_0_9_0.default = gaps SplitModeFormatter_0_8_0.default = false StackModeFormatter_0_7_0.default = default XAxisTitleFormatter_0_6_1.default = time
In this entry the line you would want to edit is the "ChartTypeFormatter_0_4_0.default = line" entry to have the type that you are looking for.
Yes, you can change the chart type for a previously saved search via the UI.
Open up the saved search you previously created. You can do this by selecting it from the Searches and Reports dropdown from the search interface, or from Splunk Manager (Searches and Reports) and clicking "Run"
Your search should open in the report builder. Click the "Edit Report" button.
Change your chart type, or any other properties you wish and click the "Apply" button
Click "Save" -> "Save report"
Essentially the above does the same thing described by the zscgeek on the back-end (edits the viewstate), but via the UI.
This doesn't seem to work for saved searches saved from flashtimeline or Manager (or from the conf files directly).